// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2012 Alexander Block.  All rights reserved.
 */

#include <linux/bsearch.h>
#include <linux/falloc.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/sort.h>
#include <linux/mount.h>
#include <linux/xattr.h>
#include <linux/posix_acl_xattr.h>
#include <linux/radix-tree.h>
#include <linux/vmalloc.h>
#include <linux/string.h>
#include <linux/compat.h>
#include <linux/crc32c.h>
#include <linux/fsverity.h>
#include "send.h"
#include "ctree.h"
#include "backref.h"
#include "locking.h"
#include "disk-io.h"
#include "btrfs_inode.h"
#include "transaction.h"
#include "compression.h"
#include "print-tree.h"
#include "accessors.h"
#include "dir-item.h"
#include "file-item.h"
#include "ioctl.h"
#include "verity.h"
#include "lru_cache.h"

/*
 * Maximum number of references an extent can have in order for us to attempt to
 * issue clone operations instead of write operations. This currently exists to
 * avoid hitting limitations of the backreference walking code (taking a lot of
 * time and using too much memory for extents with large number of references).
 */
#define SEND_MAX_EXTENT_REFS    1024

/*
 * A fs_path is a helper to dynamically build path names with unknown size.
 * It reallocates the internal buffer on demand.
 * It allows fast adding of path elements on the right side (normal path) and
 * fast adding to the left side (reversed path). A reversed path can also be
 * unreversed if needed.
 *
 * The definition of struct fs_path relies on -fms-extensions to allow
 * including a tagged struct as an anonymous member.
 */
struct __fs_path {
        char *start;
        char *end;

        char *buf;
        unsigned short buf_len:15;
        unsigned short reversed:1;
};
static_assert(sizeof(struct __fs_path) < 256);
struct fs_path {
        struct __fs_path;
        /*
         * Average path length does not exceed 200 bytes, we'll have
         * better packing in the slab and higher chance to satisfy
         * an allocation later during send.
         */
        char inline_buf[256 - sizeof(struct __fs_path)];
};
#define FS_PATH_INLINE_SIZE \
        sizeof_field(struct fs_path, inline_buf)


/* reused for each extent */
struct clone_root {
        struct btrfs_root *root;
        u64 ino;
        u64 offset;
        u64 num_bytes;
        bool found_ref;
};

#define SEND_MAX_NAME_CACHE_SIZE                        256

/*
 * Limit the root_ids array of struct backref_cache_entry to 17 elements.
 * This makes the size of a cache entry to be exactly 192 bytes on x86_64, which
 * can be satisfied from the kmalloc-192 slab, without wasting any space.
 * The most common case is to have a single root for cloning, which corresponds
 * to the send root. Having the user specify more than 16 clone roots is not
 * common, and in such rare cases we simply don't use caching if the number of
 * cloning roots that lead down to a leaf is more than 17.
 */
#define SEND_MAX_BACKREF_CACHE_ROOTS                    17

/*
 * Max number of entries in the cache.
 * With SEND_MAX_BACKREF_CACHE_ROOTS as 17, the size in bytes, excluding
 * maple tree's internal nodes, is 24K.
 */
#define SEND_MAX_BACKREF_CACHE_SIZE 128

/*
 * A backref cache entry maps a leaf to a list of IDs of roots from which the
 * leaf is accessible and we can use for clone operations.
 * With SEND_MAX_BACKREF_CACHE_ROOTS as 12, each cache entry is 128 bytes (on
 * x86_64).
 */
struct backref_cache_entry {
        struct btrfs_lru_cache_entry entry;
        u64 root_ids[SEND_MAX_BACKREF_CACHE_ROOTS];
        /* Number of valid elements in the root_ids array. */
        int num_roots;
};

/* See the comment at lru_cache.h about struct btrfs_lru_cache_entry. */
static_assert(offsetof(struct backref_cache_entry, entry) == 0);

/*
 * Max number of entries in the cache that stores directories that were already
 * created. The cache uses raw struct btrfs_lru_cache_entry entries, so it uses
 * at most 4096 bytes - sizeof(struct btrfs_lru_cache_entry) is 48 bytes, but
 * the kmalloc-64 slab is used, so we get 4096 bytes (64 bytes * 64).
 */
#define SEND_MAX_DIR_CREATED_CACHE_SIZE                 64

/*
 * Max number of entries in the cache that stores directories that were already
 * created. The cache uses raw struct btrfs_lru_cache_entry entries, so it uses
 * at most 4096 bytes - sizeof(struct btrfs_lru_cache_entry) is 48 bytes, but
 * the kmalloc-64 slab is used, so we get 4096 bytes (64 bytes * 64).
 */
#define SEND_MAX_DIR_UTIMES_CACHE_SIZE                  64

struct send_ctx {
        struct file *send_filp;
        loff_t send_off;
        char *send_buf;
        u32 send_size;
        u32 send_max_size;
        /*
         * Whether BTRFS_SEND_A_DATA attribute was already added to current
         * command (since protocol v2, data must be the last attribute).
         */
        bool put_data;
        struct page **send_buf_pages;
        u64 flags;      /* 'flags' member of btrfs_ioctl_send_args is u64 */
        /* Protocol version compatibility requested */
        u32 proto;

        struct btrfs_root *send_root;
        struct btrfs_root *parent_root;
        struct clone_root *clone_roots;
        int clone_roots_cnt;

        /* current state of the compare_tree call */
        struct btrfs_path *left_path;
        struct btrfs_path *right_path;
        struct btrfs_key *cmp_key;

        /*
         * Keep track of the generation of the last transaction that was used
         * for relocating a block group. This is periodically checked in order
         * to detect if a relocation happened since the last check, so that we
         * don't operate on stale extent buffers for nodes (level >= 1) or on
         * stale disk_bytenr values of file extent items.
         */
        u64 last_reloc_trans;

        /*
         * infos of the currently processed inode. In case of deleted inodes,
         * these are the values from the deleted inode.
         */
        u64 cur_ino;
        u64 cur_inode_gen;
        u64 cur_inode_size;
        u64 cur_inode_mode;
        u64 cur_inode_rdev;
        u64 cur_inode_last_extent;
        u64 cur_inode_next_write_offset;
        bool cur_inode_new;
        bool cur_inode_new_gen;
        bool cur_inode_deleted;
        bool ignore_cur_inode;
        bool cur_inode_needs_verity;
        void *verity_descriptor;

        u64 send_progress;

        struct list_head new_refs;
        struct list_head deleted_refs;

        struct btrfs_lru_cache name_cache;

        /*
         * The inode we are currently processing. It's not NULL only when we
         * need to issue write commands for data extents from this inode.
         */
        struct inode *cur_inode;
        struct file_ra_state ra;
        u64 page_cache_clear_start;
        bool clean_page_cache;

        /*
         * We process inodes by their increasing order, so if before an
         * incremental send we reverse the parent/child relationship of
         * directories such that a directory with a lower inode number was
         * the parent of a directory with a higher inode number, and the one
         * becoming the new parent got renamed too, we can't rename/move the
         * directory with lower inode number when we finish processing it - we
         * must process the directory with higher inode number first, then
         * rename/move it and then rename/move the directory with lower inode
         * number. Example follows.
         *
         * Tree state when the first send was performed:
         *
         * .
         * |-- a                   (ino 257)
         *     |-- b               (ino 258)
         *         |
         *         |
         *         |-- c           (ino 259)
         *         |   |-- d       (ino 260)
         *         |
         *         |-- c2          (ino 261)
         *
         * Tree state when the second (incremental) send is performed:
         *
         * .
         * |-- a                   (ino 257)
         *     |-- b               (ino 258)
         *         |-- c2          (ino 261)
         *             |-- d2      (ino 260)
         *                 |-- cc  (ino 259)
         *
         * The sequence of steps that lead to the second state was:
         *
         * mv /a/b/c/d /a/b/c2/d2
         * mv /a/b/c /a/b/c2/d2/cc
         *
         * "c" has lower inode number, but we can't move it (2nd mv operation)
         * before we move "d", which has higher inode number.
         *
         * So we just memorize which move/rename operations must be performed
         * later when their respective parent is processed and moved/renamed.
         */

        /* Indexed by parent directory inode number. */
        struct rb_root pending_dir_moves;

        /*
         * Reverse index, indexed by the inode number of a directory that
         * is waiting for the move/rename of its immediate parent before its
         * own move/rename can be performed.
         */
        struct rb_root waiting_dir_moves;

        /*
         * A directory that is going to be rm'ed might have a child directory
         * which is in the pending directory moves index above. In this case,
         * the directory can only be removed after the move/rename of its child
         * is performed. Example:
         *
         * Parent snapshot:
         *
         * .                        (ino 256)
         * |-- a/                   (ino 257)
         *     |-- b/               (ino 258)
         *         |-- c/           (ino 259)
         *         |   |-- x/       (ino 260)
         *         |
         *         |-- y/           (ino 261)
         *
         * Send snapshot:
         *
         * .                        (ino 256)
         * |-- a/                   (ino 257)
         *     |-- b/               (ino 258)
         *         |-- YY/          (ino 261)
         *              |-- x/      (ino 260)
         *
         * Sequence of steps that lead to the send snapshot:
         * rm -f /a/b/c/foo.txt
         * mv /a/b/y /a/b/YY
         * mv /a/b/c/x /a/b/YY
         * rmdir /a/b/c
         *
         * When the child is processed, its move/rename is delayed until its
         * parent is processed (as explained above), but all other operations
         * like update utimes, chown, chgrp, etc, are performed and the paths
         * that it uses for those operations must use the orphanized name of
         * its parent (the directory we're going to rm later), so we need to
         * memorize that name.
         *
         * Indexed by the inode number of the directory to be deleted.
         */
        struct rb_root orphan_dirs;

        struct rb_root rbtree_new_refs;
        struct rb_root rbtree_deleted_refs;

        struct btrfs_lru_cache backref_cache;
        u64 backref_cache_last_reloc_trans;

        struct btrfs_lru_cache dir_created_cache;
        struct btrfs_lru_cache dir_utimes_cache;

        struct fs_path cur_inode_path;
};

struct pending_dir_move {
        struct rb_node node;
        struct list_head list;
        u64 parent_ino;
        u64 ino;
        u64 gen;
        struct list_head update_refs;
};

struct waiting_dir_move {
        struct rb_node node;
        u64 ino;
        /*
         * There might be some directory that could not be removed because it
         * was waiting for this directory inode to be moved first. Therefore
         * after this directory is moved, we can try to rmdir the ino rmdir_ino.
         */
        u64 rmdir_ino;
        u64 rmdir_gen;
        bool orphanized;
};

struct orphan_dir_info {
        struct rb_node node;
        u64 ino;
        u64 gen;
        u64 last_dir_index_offset;
        u64 dir_high_seq_ino;
};

struct name_cache_entry {
        /*
         * The key in the entry is an inode number, and the generation matches
         * the inode's generation.
         */
        struct btrfs_lru_cache_entry entry;
        u64 parent_ino;
        u64 parent_gen;
        int ret;
        int need_later_update;
        /* Name length without NUL terminator. */
        int name_len;
        /* Not NUL terminated. */
        char name[] __counted_by(name_len) __nonstring;
};

/* See the comment at lru_cache.h about struct btrfs_lru_cache_entry. */
static_assert(offsetof(struct name_cache_entry, entry) == 0);

#define ADVANCE                                                 1
#define ADVANCE_ONLY_NEXT                                       -1

enum btrfs_compare_tree_result {
        BTRFS_COMPARE_TREE_NEW,
        BTRFS_COMPARE_TREE_DELETED,
        BTRFS_COMPARE_TREE_CHANGED,
        BTRFS_COMPARE_TREE_SAME,
};

__cold
static void inconsistent_snapshot_error(struct send_ctx *sctx,
                                        enum btrfs_compare_tree_result result,
                                        const char *what)
{
        const char *result_string;

        switch (result) {
        case BTRFS_COMPARE_TREE_NEW:
                result_string = "new";
                break;
        case BTRFS_COMPARE_TREE_DELETED:
                result_string = "deleted";
                break;
        case BTRFS_COMPARE_TREE_CHANGED:
                result_string = "updated";
                break;
        case BTRFS_COMPARE_TREE_SAME:
                DEBUG_WARN("no change between trees");
                result_string = "unchanged";
                break;
        default:
                DEBUG_WARN("unexpected comparison result %d", result);
                result_string = "unexpected";
        }

        btrfs_err(sctx->send_root->fs_info,
                  "Send: inconsistent snapshot, found %s %s for inode %llu without updated inode item, send root is %llu, parent root is %llu",
                  result_string, what, sctx->cmp_key->objectid,
                  btrfs_root_id(sctx->send_root),
                  (sctx->parent_root ?  btrfs_root_id(sctx->parent_root) : 0));
}

__maybe_unused
static bool proto_cmd_ok(const struct send_ctx *sctx, int cmd)
{
        switch (sctx->proto) {
        case 1:  return cmd <= BTRFS_SEND_C_MAX_V1;
        case 2:  return cmd <= BTRFS_SEND_C_MAX_V2;
        case 3:  return cmd <= BTRFS_SEND_C_MAX_V3;
        default: return false;
        }
}

static int is_waiting_for_move(struct send_ctx *sctx, u64 ino);

static struct waiting_dir_move *
get_waiting_dir_move(struct send_ctx *sctx, u64 ino);

static int is_waiting_for_rm(struct send_ctx *sctx, u64 dir_ino, u64 gen);

static int need_send_hole(struct send_ctx *sctx)
{
        return (sctx->parent_root && !sctx->cur_inode_new &&
                !sctx->cur_inode_new_gen && !sctx->cur_inode_deleted &&
                S_ISREG(sctx->cur_inode_mode));
}

static void fs_path_reset(struct fs_path *p)
{
        if (p->reversed)
                p->start = p->buf + p->buf_len - 1;
        else
                p->start = p->buf;

        p->end = p->start;
        *p->start = 0;
}

static void init_path(struct fs_path *p)
{
        p->reversed = 0;
        p->buf = p->inline_buf;
        p->buf_len = FS_PATH_INLINE_SIZE;
        fs_path_reset(p);
}

static struct fs_path *fs_path_alloc(void)
{
        struct fs_path *p;

        p = kmalloc_obj(*p);
        if (!p)
                return NULL;
        init_path(p);
        return p;
}

static struct fs_path *fs_path_alloc_reversed(void)
{
        struct fs_path *p;

        p = fs_path_alloc();
        if (!p)
                return NULL;
        p->reversed = 1;
        fs_path_reset(p);
        return p;
}

static void fs_path_free(struct fs_path *p)
{
        if (!p)
                return;
        if (p->buf != p->inline_buf)
                kfree(p->buf);
        kfree(p);
}

static inline int fs_path_len(const struct fs_path *p)
{
        return p->end - p->start;
}

static int fs_path_ensure_buf(struct fs_path *p, int len)
{
        char *tmp_buf;
        int path_len;
        int old_buf_len;

        len++;

        if (p->buf_len >= len)
                return 0;

        if (WARN_ON(len > PATH_MAX))
                return -ENAMETOOLONG;

        path_len = fs_path_len(p);
        old_buf_len = p->buf_len;

        /*
         * Allocate to the next largest kmalloc bucket size, to let
         * the fast path happen most of the time.
         */
        len = kmalloc_size_roundup(len);
        /*
         * First time the inline_buf does not suffice
         */
        if (p->buf == p->inline_buf) {
                tmp_buf = kmalloc(len, GFP_KERNEL);
                if (tmp_buf)
                        memcpy(tmp_buf, p->buf, old_buf_len);
        } else {
                tmp_buf = krealloc(p->buf, len, GFP_KERNEL);
        }
        if (!tmp_buf)
                return -ENOMEM;
        p->buf = tmp_buf;
        p->buf_len = len;

        if (p->reversed) {
                tmp_buf = p->buf + old_buf_len - path_len - 1;
                p->end = p->buf + p->buf_len - 1;
                p->start = p->end - path_len;
                memmove(p->start, tmp_buf, path_len + 1);
        } else {
                p->start = p->buf;
                p->end = p->start + path_len;
        }
        return 0;
}

static int fs_path_prepare_for_add(struct fs_path *p, int name_len,
                                   char **prepared)
{
        int ret;
        int new_len;

        new_len = fs_path_len(p) + name_len;
        if (p->start != p->end)
                new_len++;
        ret = fs_path_ensure_buf(p, new_len);
        if (ret < 0)
                return ret;

        if (p->reversed) {
                if (p->start != p->end)
                        *--p->start = '/';
                p->start -= name_len;
                *prepared = p->start;
        } else {
                if (p->start != p->end)
                        *p->end++ = '/';
                *prepared = p->end;
                p->end += name_len;
                *p->end = 0;
        }

        return 0;
}

static int fs_path_add(struct fs_path *p, const char *name, int name_len)
{
        int ret;
        char *prepared;

        ret = fs_path_prepare_for_add(p, name_len, &prepared);
        if (ret < 0)
                return ret;
        memcpy(prepared, name, name_len);

        return 0;
}

static inline int fs_path_add_path(struct fs_path *p, const struct fs_path *p2)
{
        return fs_path_add(p, p2->start, fs_path_len(p2));
}

static int fs_path_add_from_extent_buffer(struct fs_path *p,
                                          struct extent_buffer *eb,
                                          unsigned long off, int len)
{
        int ret;
        char *prepared;

        ret = fs_path_prepare_for_add(p, len, &prepared);
        if (ret < 0)
                return ret;

        read_extent_buffer(eb, prepared, off, len);

        return 0;
}

static int fs_path_copy(struct fs_path *p, struct fs_path *from)
{
        p->reversed = from->reversed;
        fs_path_reset(p);

        return fs_path_add_path(p, from);
}

static void fs_path_unreverse(struct fs_path *p)
{
        char *tmp;
        int len;

        if (!p->reversed)
                return;

        tmp = p->start;
        len = fs_path_len(p);
        p->start = p->buf;
        p->end = p->start + len;
        memmove(p->start, tmp, len + 1);
        p->reversed = 0;
}

static inline bool is_current_inode_path(const struct send_ctx *sctx,
                                         const struct fs_path *path)
{
        const struct fs_path *cur = &sctx->cur_inode_path;

        return (strncmp(path->start, cur->start, fs_path_len(cur)) == 0);
}

static struct btrfs_path *alloc_path_for_send(void)
{
        struct btrfs_path *path;

        path = btrfs_alloc_path();
        if (!path)
                return NULL;
        path->search_commit_root = true;
        path->skip_locking = true;
        path->need_commit_sem = true;
        return path;
}

static int write_buf(struct file *filp, const void *buf, u32 len, loff_t *off)
{
        int ret;
        u32 pos = 0;

        while (pos < len) {
                ret = kernel_write(filp, buf + pos, len - pos, off);
                if (ret < 0)
                        return ret;
                if (unlikely(ret == 0))
                        return -EIO;
                pos += ret;
        }

        return 0;
}

static int tlv_put(struct send_ctx *sctx, u16 attr, const void *data, int len)
{
        struct btrfs_tlv_header *hdr;
        int total_len = sizeof(*hdr) + len;
        int left = sctx->send_max_size - sctx->send_size;

        if (WARN_ON_ONCE(sctx->put_data))
                return -EINVAL;

        if (unlikely(left < total_len))
                return -EOVERFLOW;

        hdr = (struct btrfs_tlv_header *) (sctx->send_buf + sctx->send_size);
        put_unaligned_le16(attr, &hdr->tlv_type);
        put_unaligned_le16(len, &hdr->tlv_len);
        memcpy(hdr + 1, data, len);
        sctx->send_size += total_len;

        return 0;
}

#define TLV_PUT_DEFINE_INT(bits) \
        static int tlv_put_u##bits(struct send_ctx *sctx,               \
                        u##bits attr, u##bits value)                    \
        {                                                               \
                __le##bits __tmp = cpu_to_le##bits(value);              \
                return tlv_put(sctx, attr, &__tmp, sizeof(__tmp));      \
        }

TLV_PUT_DEFINE_INT(8)
TLV_PUT_DEFINE_INT(32)
TLV_PUT_DEFINE_INT(64)

static int tlv_put_string(struct send_ctx *sctx, u16 attr,
                          const char *str, int len)
{
        if (len == -1)
                len = strlen(str);
        return tlv_put(sctx, attr, str, len);
}

static int tlv_put_uuid(struct send_ctx *sctx, u16 attr,
                        const u8 *uuid)
{
        return tlv_put(sctx, attr, uuid, BTRFS_UUID_SIZE);
}

static int tlv_put_btrfs_timespec(struct send_ctx *sctx, u16 attr,
                                  struct extent_buffer *eb,
                                  struct btrfs_timespec *ts)
{
        struct btrfs_timespec bts;
        read_extent_buffer(eb, &bts, (unsigned long)ts, sizeof(bts));
        return tlv_put(sctx, attr, &bts, sizeof(bts));
}


#define TLV_PUT(sctx, attrtype, data, attrlen) \
        do { \
                ret = tlv_put(sctx, attrtype, data, attrlen); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)

#define TLV_PUT_INT(sctx, attrtype, bits, value) \
        do { \
                ret = tlv_put_u##bits(sctx, attrtype, value); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)

#define TLV_PUT_U8(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 8, data)
#define TLV_PUT_U16(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 16, data)
#define TLV_PUT_U32(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 32, data)
#define TLV_PUT_U64(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 64, data)
#define TLV_PUT_STRING(sctx, attrtype, str, len) \
        do { \
                ret = tlv_put_string(sctx, attrtype, str, len); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)
#define TLV_PUT_PATH(sctx, attrtype, p) \
        do { \
                ret = tlv_put_string(sctx, attrtype, p->start, \
                                     fs_path_len((p)));        \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while(0)
#define TLV_PUT_UUID(sctx, attrtype, uuid) \
        do { \
                ret = tlv_put_uuid(sctx, attrtype, uuid); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)
#define TLV_PUT_BTRFS_TIMESPEC(sctx, attrtype, eb, ts) \
        do { \
                ret = tlv_put_btrfs_timespec(sctx, attrtype, eb, ts); \
                if (ret < 0) \
                        goto tlv_put_failure; \
        } while (0)

static int send_header(struct send_ctx *sctx)
{
        struct btrfs_stream_header hdr;

        strscpy(hdr.magic, BTRFS_SEND_STREAM_MAGIC);
        hdr.version = cpu_to_le32(sctx->proto);
        return write_buf(sctx->send_filp, &hdr, sizeof(hdr),
                                        &sctx->send_off);
}

/*
 * For each command/item we want to send to userspace, we call this function.
 */
static int begin_cmd(struct send_ctx *sctx, int cmd)
{
        struct btrfs_cmd_header *hdr;

        if (WARN_ON(!sctx->send_buf))
                return -EINVAL;

        if (unlikely(sctx->send_size != 0)) {
                btrfs_err(sctx->send_root->fs_info,
                          "send: command header buffer not empty cmd %d offset %llu",
                          cmd, sctx->send_off);
                return -EINVAL;
        }

        sctx->send_size += sizeof(*hdr);
        hdr = (struct btrfs_cmd_header *)sctx->send_buf;
        put_unaligned_le16(cmd, &hdr->cmd);

        return 0;
}

static int send_cmd(struct send_ctx *sctx)
{
        int ret;
        struct btrfs_cmd_header *hdr;
        u32 crc;

        hdr = (struct btrfs_cmd_header *)sctx->send_buf;
        put_unaligned_le32(sctx->send_size - sizeof(*hdr), &hdr->len);
        put_unaligned_le32(0, &hdr->crc);

        crc = crc32c(0, (unsigned char *)sctx->send_buf, sctx->send_size);
        put_unaligned_le32(crc, &hdr->crc);

        ret = write_buf(sctx->send_filp, sctx->send_buf, sctx->send_size,
                                        &sctx->send_off);

        sctx->send_size = 0;
        sctx->put_data = false;

        return ret;
}

/*
 * Sends a move instruction to user space
 */
static int send_rename(struct send_ctx *sctx,
                     struct fs_path *from, struct fs_path *to)
{
        int ret;

        ret = begin_cmd(sctx, BTRFS_SEND_C_RENAME);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, from);
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_TO, to);

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

/*
 * Sends a link instruction to user space
 */
static int send_link(struct send_ctx *sctx,
                     struct fs_path *path, struct fs_path *lnk)
{
        int ret;

        ret = begin_cmd(sctx, BTRFS_SEND_C_LINK);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_LINK, lnk);

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

/*
 * Sends an unlink instruction to user space
 */
static int send_unlink(struct send_ctx *sctx, struct fs_path *path)
{
        int ret;

        ret = begin_cmd(sctx, BTRFS_SEND_C_UNLINK);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

/*
 * Sends a rmdir instruction to user space
 */
static int send_rmdir(struct send_ctx *sctx, struct fs_path *path)
{
        int ret;

        ret = begin_cmd(sctx, BTRFS_SEND_C_RMDIR);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

struct btrfs_inode_info {
        u64 size;
        u64 gen;
        u64 mode;
        u64 uid;
        u64 gid;
        u64 rdev;
        u64 fileattr;
        u64 nlink;
};

/*
 * Helper function to retrieve some fields from an inode item.
 */
static int get_inode_info(struct btrfs_root *root, u64 ino,
                          struct btrfs_inode_info *info)
{
        int ret;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_inode_item *ii;
        struct btrfs_key key;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = ino;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret) {
                if (ret > 0)
                        ret = -ENOENT;
                return ret;
        }

        if (!info)
                return 0;

        ii = btrfs_item_ptr(path->nodes[0], path->slots[0],
                        struct btrfs_inode_item);
        info->size = btrfs_inode_size(path->nodes[0], ii);
        info->gen = btrfs_inode_generation(path->nodes[0], ii);
        info->mode = btrfs_inode_mode(path->nodes[0], ii);
        info->uid = btrfs_inode_uid(path->nodes[0], ii);
        info->gid = btrfs_inode_gid(path->nodes[0], ii);
        info->rdev = btrfs_inode_rdev(path->nodes[0], ii);
        info->nlink = btrfs_inode_nlink(path->nodes[0], ii);
        /*
         * Transfer the unchanged u64 value of btrfs_inode_item::flags, that's
         * otherwise logically split to 32/32 parts.
         */
        info->fileattr = btrfs_inode_flags(path->nodes[0], ii);

        return 0;
}

static int get_inode_gen(struct btrfs_root *root, u64 ino, u64 *gen)
{
        int ret;
        struct btrfs_inode_info info = { 0 };

        ASSERT(gen);

        ret = get_inode_info(root, ino, &info);
        *gen = info.gen;
        return ret;
}

typedef int (*iterate_inode_ref_t)(u64 dir, struct fs_path *p, void *ctx);

/*
 * Helper function to iterate the entries in ONE btrfs_inode_ref or
 * btrfs_inode_extref.
 * The iterate callback may return a non zero value to stop iteration. This can
 * be a negative value for error codes or 1 to simply stop it.
 *
 * path must point to the INODE_REF or INODE_EXTREF when called.
 */
static int iterate_inode_ref(struct btrfs_root *root, struct btrfs_path *path,
                             struct btrfs_key *found_key, bool resolve,
                             iterate_inode_ref_t iterate, void *ctx)
{
        struct extent_buffer *eb = path->nodes[0];
        struct btrfs_inode_ref *iref;
        struct btrfs_inode_extref *extref;
        BTRFS_PATH_AUTO_FREE(tmp_path);
        struct fs_path *p;
        u32 cur = 0;
        u32 total;
        int slot = path->slots[0];
        u32 name_len;
        char *start;
        int ret = 0;
        u64 dir;
        unsigned long name_off;
        unsigned long elem_size;
        unsigned long ptr;

        p = fs_path_alloc_reversed();
        if (!p)
                return -ENOMEM;

        tmp_path = alloc_path_for_send();
        if (!tmp_path) {
                fs_path_free(p);
                return -ENOMEM;
        }


        if (found_key->type == BTRFS_INODE_REF_KEY) {
                ptr = (unsigned long)btrfs_item_ptr(eb, slot,
                                                    struct btrfs_inode_ref);
                total = btrfs_item_size(eb, slot);
                elem_size = sizeof(*iref);
        } else {
                ptr = btrfs_item_ptr_offset(eb, slot);
                total = btrfs_item_size(eb, slot);
                elem_size = sizeof(*extref);
        }

        while (cur < total) {
                fs_path_reset(p);

                if (found_key->type == BTRFS_INODE_REF_KEY) {
                        iref = (struct btrfs_inode_ref *)(ptr + cur);
                        name_len = btrfs_inode_ref_name_len(eb, iref);
                        name_off = (unsigned long)(iref + 1);
                        dir = found_key->offset;
                } else {
                        extref = (struct btrfs_inode_extref *)(ptr + cur);
                        name_len = btrfs_inode_extref_name_len(eb, extref);
                        name_off = (unsigned long)&extref->name;
                        dir = btrfs_inode_extref_parent(eb, extref);
                }

                if (resolve) {
                        start = btrfs_ref_to_path(root, tmp_path, name_len,
                                                  name_off, eb, dir,
                                                  p->buf, p->buf_len);
                        if (IS_ERR(start)) {
                                ret = PTR_ERR(start);
                                goto out;
                        }
                        if (start < p->buf) {
                                /* overflow , try again with larger buffer */
                                ret = fs_path_ensure_buf(p,
                                                p->buf_len + p->buf - start);
                                if (ret < 0)
                                        goto out;
                                start = btrfs_ref_to_path(root, tmp_path,
                                                          name_len, name_off,
                                                          eb, dir,
                                                          p->buf, p->buf_len);
                                if (IS_ERR(start)) {
                                        ret = PTR_ERR(start);
                                        goto out;
                                }
                                if (unlikely(start < p->buf)) {
                                        btrfs_err(root->fs_info,
                          "send: path ref buffer underflow for key " BTRFS_KEY_FMT,
                                                  BTRFS_KEY_FMT_VALUE(found_key));
                                        ret = -EINVAL;
                                        goto out;
                                }
                        }
                        p->start = start;
                } else {
                        ret = fs_path_add_from_extent_buffer(p, eb, name_off,
                                                             name_len);
                        if (ret < 0)
                                goto out;
                }

                cur += elem_size + name_len;
                ret = iterate(dir, p, ctx);
                if (ret)
                        goto out;
        }

out:
        fs_path_free(p);
        return ret;
}

typedef int (*iterate_dir_item_t)(int num, struct btrfs_key *di_key,
                                  const char *name, int name_len,
                                  const char *data, int data_len,
                                  void *ctx);

/*
 * Helper function to iterate the entries in ONE btrfs_dir_item.
 * The iterate callback may return a non zero value to stop iteration. This can
 * be a negative value for error codes or 1 to simply stop it.
 *
 * path must point to the dir item when called.
 */
static int iterate_dir_item(struct btrfs_root *root, struct btrfs_path *path,
                            iterate_dir_item_t iterate, void *ctx)
{
        int ret = 0;
        struct extent_buffer *eb;
        struct btrfs_dir_item *di;
        struct btrfs_key di_key;
        char *buf = NULL;
        int buf_len;
        u32 name_len;
        u32 data_len;
        u32 cur;
        u32 len;
        u32 total;
        int slot;
        int num;

        /*
         * Start with a small buffer (1 page). If later we end up needing more
         * space, which can happen for xattrs on a fs with a leaf size greater
         * than the page size, attempt to increase the buffer. Typically xattr
         * values are small.
         */
        buf_len = PATH_MAX;
        buf = kmalloc(buf_len, GFP_KERNEL);
        if (!buf) {
                ret = -ENOMEM;
                goto out;
        }

        eb = path->nodes[0];
        slot = path->slots[0];
        di = btrfs_item_ptr(eb, slot, struct btrfs_dir_item);
        cur = 0;
        len = 0;
        total = btrfs_item_size(eb, slot);

        num = 0;
        while (cur < total) {
                name_len = btrfs_dir_name_len(eb, di);
                data_len = btrfs_dir_data_len(eb, di);
                btrfs_dir_item_key_to_cpu(eb, di, &di_key);

                if (btrfs_dir_ftype(eb, di) == BTRFS_FT_XATTR) {
                        if (unlikely(name_len > XATTR_NAME_MAX)) {
                                ret = -ENAMETOOLONG;
                                goto out;
                        }
                        if (unlikely(name_len + data_len >
                                     BTRFS_MAX_XATTR_SIZE(root->fs_info))) {
                                ret = -E2BIG;
                                goto out;
                        }
                } else {
                        /*
                         * Path too long
                         */
                        if (unlikely(name_len + data_len > PATH_MAX)) {
                                ret = -ENAMETOOLONG;
                                goto out;
                        }
                }

                if (name_len + data_len > buf_len) {
                        buf_len = name_len + data_len;
                        if (is_vmalloc_addr(buf)) {
                                vfree(buf);
                                buf = NULL;
                        } else {
                                char *tmp = krealloc(buf, buf_len,
                                                GFP_KERNEL | __GFP_NOWARN);

                                if (!tmp)
                                        kfree(buf);
                                buf = tmp;
                        }
                        if (!buf) {
                                buf = kvmalloc(buf_len, GFP_KERNEL);
                                if (!buf) {
                                        ret = -ENOMEM;
                                        goto out;
                                }
                        }
                }

                read_extent_buffer(eb, buf, (unsigned long)(di + 1),
                                name_len + data_len);

                len = sizeof(*di) + name_len + data_len;
                di = (struct btrfs_dir_item *)((char *)di + len);
                cur += len;

                ret = iterate(num, &di_key, buf, name_len, buf + name_len,
                              data_len, ctx);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret = 0;
                        goto out;
                }

                num++;
        }

out:
        kvfree(buf);
        return ret;
}

static int __copy_first_ref(u64 dir, struct fs_path *p, void *ctx)
{
        int ret;
        struct fs_path *pt = ctx;

        ret = fs_path_copy(pt, p);
        if (ret < 0)
                return ret;

        /* we want the first only */
        return 1;
}

/*
 * Retrieve the first path of an inode. If an inode has more then one
 * ref/hardlink, this is ignored.
 */
static int get_inode_path(struct btrfs_root *root,
                          u64 ino, struct fs_path *path)
{
        int ret;
        struct btrfs_key key, found_key;
        BTRFS_PATH_AUTO_FREE(p);

        p = alloc_path_for_send();
        if (!p)
                return -ENOMEM;

        fs_path_reset(path);

        key.objectid = ino;
        key.type = BTRFS_INODE_REF_KEY;
        key.offset = 0;

        ret = btrfs_search_slot_for_read(root, &key, p, 1, 0);
        if (ret < 0)
                return ret;
        if (ret)
                return 1;

        btrfs_item_key_to_cpu(p->nodes[0], &found_key, p->slots[0]);
        if (found_key.objectid != ino ||
            (found_key.type != BTRFS_INODE_REF_KEY &&
             found_key.type != BTRFS_INODE_EXTREF_KEY))
                return -ENOENT;

        ret = iterate_inode_ref(root, p, &found_key, true, __copy_first_ref, path);
        if (ret < 0)
                return ret;
        return 0;
}

struct backref_ctx {
        struct send_ctx *sctx;

        /* number of total found references */
        u64 found;

        /*
         * used for clones found in send_root. clones found behind cur_objectid
         * and cur_offset are not considered as allowed clones.
         */
        u64 cur_objectid;
        u64 cur_offset;

        /* may be truncated in case it's the last extent in a file */
        u64 extent_len;

        /* The bytenr the file extent item we are processing refers to. */
        u64 bytenr;
        /* The owner (root id) of the data backref for the current extent. */
        u64 backref_owner;
        /* The offset of the data backref for the current extent. */
        u64 backref_offset;
};

static int __clone_root_cmp_bsearch(const void *key, const void *elt)
{
        u64 root = (u64)(uintptr_t)key;
        const struct clone_root *cr = elt;

        if (root < btrfs_root_id(cr->root))
                return -1;
        if (root > btrfs_root_id(cr->root))
                return 1;
        return 0;
}

static int __clone_root_cmp_sort(const void *e1, const void *e2)
{
        const struct clone_root *cr1 = e1;
        const struct clone_root *cr2 = e2;

        if (btrfs_root_id(cr1->root) < btrfs_root_id(cr2->root))
                return -1;
        if (btrfs_root_id(cr1->root) > btrfs_root_id(cr2->root))
                return 1;
        return 0;
}

/*
 * Called for every backref that is found for the current extent.
 * Results are collected in sctx->clone_roots->ino/offset.
 */
static int iterate_backrefs(u64 ino, u64 offset, u64 num_bytes, u64 root_id,
                            void *ctx_)
{
        struct backref_ctx *bctx = ctx_;
        struct clone_root *clone_root;

        /* First check if the root is in the list of accepted clone sources */
        clone_root = bsearch((void *)(uintptr_t)root_id, bctx->sctx->clone_roots,
                             bctx->sctx->clone_roots_cnt,
                             sizeof(struct clone_root),
                             __clone_root_cmp_bsearch);
        if (!clone_root)
                return 0;

        /* This is our own reference, bail out as we can't clone from it. */
        if (clone_root->root == bctx->sctx->send_root &&
            ino == bctx->cur_objectid &&
            offset == bctx->cur_offset)
                return 0;

        /*
         * Make sure we don't consider clones from send_root that are
         * behind the current inode/offset.
         */
        if (clone_root->root == bctx->sctx->send_root) {
                /*
                 * If the source inode was not yet processed we can't issue a
                 * clone operation, as the source extent does not exist yet at
                 * the destination of the stream.
                 */
                if (ino > bctx->cur_objectid)
                        return 0;
                /*
                 * We clone from the inode currently being sent as long as the
                 * source extent is already processed, otherwise we could try
                 * to clone from an extent that does not exist yet at the
                 * destination of the stream.
                 */
                if (ino == bctx->cur_objectid &&
                    offset + bctx->extent_len >
                    bctx->sctx->cur_inode_next_write_offset)
                        return 0;
        }

        bctx->found++;
        clone_root->found_ref = true;

        /*
         * If the given backref refers to a file extent item with a larger
         * number of bytes than what we found before, use the new one so that
         * we clone more optimally and end up doing less writes and getting
         * less exclusive, non-shared extents at the destination.
         */
        if (num_bytes > clone_root->num_bytes) {
                clone_root->ino = ino;
                clone_root->offset = offset;
                clone_root->num_bytes = num_bytes;

                /*
                 * Found a perfect candidate, so there's no need to continue
                 * backref walking.
                 */
                if (num_bytes >= bctx->extent_len)
                        return BTRFS_ITERATE_EXTENT_INODES_STOP;
        }

        return 0;
}

static bool lookup_backref_cache(u64 leaf_bytenr, void *ctx,
                                 const u64 **root_ids_ret, int *root_count_ret)
{
        struct backref_ctx *bctx = ctx;
        struct send_ctx *sctx = bctx->sctx;
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        const u64 key = leaf_bytenr >> fs_info->nodesize_bits;
        struct btrfs_lru_cache_entry *raw_entry;
        struct backref_cache_entry *entry;

        if (sctx->backref_cache.size == 0)
                return false;

        /*
         * If relocation happened since we first filled the cache, then we must
         * empty the cache and can not use it, because even though we operate on
         * read-only roots, their leaves and nodes may have been reallocated and
         * now be used for different nodes/leaves of the same tree or some other
         * tree.
         *
         * We are called from iterate_extent_inodes() while either holding a
         * transaction handle or holding fs_info->commit_root_sem, so no need
         * to take any lock here.
         */
        if (fs_info->last_reloc_trans > sctx->backref_cache_last_reloc_trans) {
                btrfs_lru_cache_clear(&sctx->backref_cache);
                return false;
        }

        raw_entry = btrfs_lru_cache_lookup(&sctx->backref_cache, key, 0);
        if (!raw_entry)
                return false;

        entry = container_of(raw_entry, struct backref_cache_entry, entry);
        *root_ids_ret = entry->root_ids;
        *root_count_ret = entry->num_roots;

        return true;
}

static void store_backref_cache(u64 leaf_bytenr, const struct ulist *root_ids,
                                void *ctx)
{
        struct backref_ctx *bctx = ctx;
        struct send_ctx *sctx = bctx->sctx;
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        struct backref_cache_entry *new_entry;
        struct ulist_iterator uiter;
        struct ulist_node *node;
        int ret;

        /*
         * We're called while holding a transaction handle or while holding
         * fs_info->commit_root_sem (at iterate_extent_inodes()), so must do a
         * NOFS allocation.
         */
        new_entry = kmalloc_obj(struct backref_cache_entry, GFP_NOFS);
        /* No worries, cache is optional. */
        if (!new_entry)
                return;

        new_entry->entry.key = leaf_bytenr >> fs_info->nodesize_bits;
        new_entry->entry.gen = 0;
        new_entry->num_roots = 0;
        ULIST_ITER_INIT(&uiter);
        while ((node = ulist_next(root_ids, &uiter)) != NULL) {
                const u64 root_id = node->val;
                struct clone_root *root;

                root = bsearch((void *)(uintptr_t)root_id, sctx->clone_roots,
                               sctx->clone_roots_cnt, sizeof(struct clone_root),
                               __clone_root_cmp_bsearch);
                if (!root)
                        continue;

                /* Too many roots, just exit, no worries as caching is optional. */
                if (new_entry->num_roots >= SEND_MAX_BACKREF_CACHE_ROOTS) {
                        kfree(new_entry);
                        return;
                }

                new_entry->root_ids[new_entry->num_roots] = root_id;
                new_entry->num_roots++;
        }

        /*
         * We may have not added any roots to the new cache entry, which means
         * none of the roots is part of the list of roots from which we are
         * allowed to clone. Cache the new entry as it's still useful to avoid
         * backref walking to determine which roots have a path to the leaf.
         *
         * Also use GFP_NOFS because we're called while holding a transaction
         * handle or while holding fs_info->commit_root_sem.
         */
        ret = btrfs_lru_cache_store(&sctx->backref_cache, &new_entry->entry,
                                    GFP_NOFS);
        ASSERT(ret == 0 || ret == -ENOMEM);
        if (ret) {
                /* Caching is optional, no worries. */
                kfree(new_entry);
                return;
        }

        /*
         * We are called from iterate_extent_inodes() while either holding a
         * transaction handle or holding fs_info->commit_root_sem, so no need
         * to take any lock here.
         */
        if (sctx->backref_cache.size == 1)
                sctx->backref_cache_last_reloc_trans = fs_info->last_reloc_trans;
}

static int check_extent_item(u64 bytenr, const struct btrfs_extent_item *ei,
                             const struct extent_buffer *leaf, void *ctx)
{
        const u64 refs = btrfs_extent_refs(leaf, ei);
        const struct backref_ctx *bctx = ctx;
        const struct send_ctx *sctx = bctx->sctx;

        if (bytenr == bctx->bytenr) {
                const u64 flags = btrfs_extent_flags(leaf, ei);

                if (WARN_ON(flags & BTRFS_EXTENT_FLAG_TREE_BLOCK))
                        return -EUCLEAN;

                /*
                 * If we have only one reference and only the send root as a
                 * clone source - meaning no clone roots were given in the
                 * struct btrfs_ioctl_send_args passed to the send ioctl - then
                 * it's our reference and there's no point in doing backref
                 * walking which is expensive, so exit early.
                 */
                if (refs == 1 && sctx->clone_roots_cnt == 1)
                        return -ENOENT;
        }

        /*
         * Backreference walking (iterate_extent_inodes() below) is currently
         * too expensive when an extent has a large number of references, both
         * in time spent and used memory. So for now just fallback to write
         * operations instead of clone operations when an extent has more than
         * a certain amount of references.
         */
        if (refs > SEND_MAX_EXTENT_REFS)
                return -ENOENT;

        return 0;
}

static bool skip_self_data_ref(u64 root, u64 ino, u64 offset, void *ctx)
{
        const struct backref_ctx *bctx = ctx;

        if (ino == bctx->cur_objectid &&
            root == bctx->backref_owner &&
            offset == bctx->backref_offset)
                return true;

        return false;
}

/*
 * Given an inode, offset and extent item, it finds a good clone for a clone
 * instruction. Returns -ENOENT when none could be found. The function makes
 * sure that the returned clone is usable at the point where sending is at the
 * moment. This means, that no clones are accepted which lie behind the current
 * inode+offset.
 *
 * path must point to the extent item when called.
 */
static int find_extent_clone(struct send_ctx *sctx,
                             struct btrfs_path *path,
                             u64 ino, u64 data_offset,
                             u64 ino_size,
                             struct clone_root **found)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret;
        int extent_type;
        u64 disk_byte;
        u64 num_bytes;
        struct btrfs_file_extent_item *fi;
        struct extent_buffer *eb = path->nodes[0];
        struct backref_ctx backref_ctx = { 0 };
        struct btrfs_backref_walk_ctx backref_walk_ctx = { 0 };
        struct clone_root *cur_clone_root;
        int compressed;
        u32 i;

        /*
         * With fallocate we can get prealloc extents beyond the inode's i_size,
         * so we don't do anything here because clone operations can not clone
         * to a range beyond i_size without increasing the i_size of the
         * destination inode.
         */
        if (data_offset >= ino_size)
                return 0;

        fi = btrfs_item_ptr(eb, path->slots[0], struct btrfs_file_extent_item);
        extent_type = btrfs_file_extent_type(eb, fi);
        if (extent_type == BTRFS_FILE_EXTENT_INLINE)
                return -ENOENT;

        disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
        if (disk_byte == 0)
                return -ENOENT;

        compressed = btrfs_file_extent_compression(eb, fi);
        num_bytes = btrfs_file_extent_num_bytes(eb, fi);

        /*
         * Setup the clone roots.
         */
        for (i = 0; i < sctx->clone_roots_cnt; i++) {
                cur_clone_root = sctx->clone_roots + i;
                cur_clone_root->ino = (u64)-1;
                cur_clone_root->offset = 0;
                cur_clone_root->num_bytes = 0;
                cur_clone_root->found_ref = false;
        }

        backref_ctx.sctx = sctx;
        backref_ctx.cur_objectid = ino;
        backref_ctx.cur_offset = data_offset;
        backref_ctx.bytenr = disk_byte;
        /*
         * Use the header owner and not the send root's id, because in case of a
         * snapshot we can have shared subtrees.
         */
        backref_ctx.backref_owner = btrfs_header_owner(eb);
        backref_ctx.backref_offset = data_offset - btrfs_file_extent_offset(eb, fi);

        /*
         * The last extent of a file may be too large due to page alignment.
         * We need to adjust extent_len in this case so that the checks in
         * iterate_backrefs() work.
         */
        if (data_offset + num_bytes >= ino_size)
                backref_ctx.extent_len = ino_size - data_offset;
        else
                backref_ctx.extent_len = num_bytes;

        /*
         * Now collect all backrefs.
         */
        backref_walk_ctx.bytenr = disk_byte;
        if (compressed == BTRFS_COMPRESS_NONE)
                backref_walk_ctx.extent_item_pos = btrfs_file_extent_offset(eb, fi);
        backref_walk_ctx.fs_info = fs_info;
        backref_walk_ctx.cache_lookup = lookup_backref_cache;
        backref_walk_ctx.cache_store = store_backref_cache;
        backref_walk_ctx.indirect_ref_iterator = iterate_backrefs;
        backref_walk_ctx.check_extent_item = check_extent_item;
        backref_walk_ctx.user_ctx = &backref_ctx;

        /*
         * If have a single clone root, then it's the send root and we can tell
         * the backref walking code to skip our own backref and not resolve it,
         * since we can not use it for cloning - the source and destination
         * ranges can't overlap and in case the leaf is shared through a subtree
         * due to snapshots, we can't use those other roots since they are not
         * in the list of clone roots.
         */
        if (sctx->clone_roots_cnt == 1)
                backref_walk_ctx.skip_data_ref = skip_self_data_ref;

        ret = iterate_extent_inodes(&backref_walk_ctx, true, iterate_backrefs,
                                    &backref_ctx);
        if (ret < 0)
                return ret;

        down_read(&fs_info->commit_root_sem);
        if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
                /*
                 * A transaction commit for a transaction in which block group
                 * relocation was done just happened.
                 * The disk_bytenr of the file extent item we processed is
                 * possibly stale, referring to the extent's location before
                 * relocation. So act as if we haven't found any clone sources
                 * and fallback to write commands, which will read the correct
                 * data from the new extent location. Otherwise we will fail
                 * below because we haven't found our own back reference or we
                 * could be getting incorrect sources in case the old extent
                 * was already reallocated after the relocation.
                 */
                up_read(&fs_info->commit_root_sem);
                return -ENOENT;
        }
        up_read(&fs_info->commit_root_sem);

        if (!backref_ctx.found)
                return -ENOENT;

        cur_clone_root = NULL;
        for (i = 0; i < sctx->clone_roots_cnt; i++) {
                struct clone_root *clone_root = &sctx->clone_roots[i];

                if (!clone_root->found_ref)
                        continue;

                /*
                 * Choose the root from which we can clone more bytes, to
                 * minimize write operations and therefore have more extent
                 * sharing at the destination (the same as in the source).
                 */
                if (!cur_clone_root ||
                    clone_root->num_bytes > cur_clone_root->num_bytes) {
                        cur_clone_root = clone_root;

                        /*
                         * We found an optimal clone candidate (any inode from
                         * any root is fine), so we're done.
                         */
                        if (clone_root->num_bytes >= backref_ctx.extent_len)
                                break;
                }
        }

        if (cur_clone_root) {
                *found = cur_clone_root;
                ret = 0;
        } else {
                ret = -ENOENT;
        }

        return ret;
}

static int read_symlink(struct btrfs_root *root,
                        u64 ino,
                        struct fs_path *dest)
{
        int ret;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct btrfs_file_extent_item *ei;
        u8 type;
        u8 compression;
        unsigned long off;
        int len;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                return ret;
        if (unlikely(ret)) {
                /*
                 * An empty symlink inode. Can happen in rare error paths when
                 * creating a symlink (transaction committed before the inode
                 * eviction handler removed the symlink inode items and a crash
                 * happened in between or the subvol was snapshotted in between).
                 * Print an informative message to dmesg/syslog so that the user
                 * can delete the symlink.
                 */
                btrfs_err(root->fs_info,
                          "Found empty symlink inode %llu at root %llu",
                          ino, btrfs_root_id(root));
                return -EIO;
        }

        ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                        struct btrfs_file_extent_item);
        type = btrfs_file_extent_type(path->nodes[0], ei);
        if (unlikely(type != BTRFS_FILE_EXTENT_INLINE)) {
                ret = -EUCLEAN;
                btrfs_crit(root->fs_info,
"send: found symlink extent that is not inline, ino %llu root %llu extent type %d",
                           ino, btrfs_root_id(root), type);
                return ret;
        }
        compression = btrfs_file_extent_compression(path->nodes[0], ei);
        if (unlikely(compression != BTRFS_COMPRESS_NONE)) {
                ret = -EUCLEAN;
                btrfs_crit(root->fs_info,
"send: found symlink extent with compression, ino %llu root %llu compression type %d",
                           ino, btrfs_root_id(root), compression);
                return ret;
        }

        off = btrfs_file_extent_inline_start(ei);
        len = btrfs_file_extent_ram_bytes(path->nodes[0], ei);

        return fs_path_add_from_extent_buffer(dest, path->nodes[0], off, len);
}

/*
 * Helper function to generate a file name that is unique in the root of
 * send_root and parent_root. This is used to generate names for orphan inodes.
 */
static int gen_unique_name(struct send_ctx *sctx,
                           u64 ino, u64 gen,
                           struct fs_path *dest)
{
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_dir_item *di;
        char tmp[64];
        int len;
        u64 idx = 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        while (1) {
                struct fscrypt_str tmp_name;

                len = snprintf(tmp, sizeof(tmp), "o%llu-%llu-%llu",
                                ino, gen, idx);
                ASSERT(len < sizeof(tmp));
                tmp_name.name = tmp;
                tmp_name.len = len;

                di = btrfs_lookup_dir_item(NULL, sctx->send_root,
                                path, BTRFS_FIRST_FREE_OBJECTID,
                                &tmp_name, 0);
                btrfs_release_path(path);
                if (IS_ERR(di))
                        return PTR_ERR(di);

                if (di) {
                        /* not unique, try again */
                        idx++;
                        continue;
                }

                if (!sctx->parent_root) {
                        /* unique */
                        break;
                }

                di = btrfs_lookup_dir_item(NULL, sctx->parent_root,
                                path, BTRFS_FIRST_FREE_OBJECTID,
                                &tmp_name, 0);
                btrfs_release_path(path);
                if (IS_ERR(di))
                        return PTR_ERR(di);

                if (di) {
                        /* not unique, try again */
                        idx++;
                        continue;
                }
                /* unique */
                break;
        }

        return fs_path_add(dest, tmp, len);
}

enum inode_state {
        inode_state_no_change,
        inode_state_will_create,
        inode_state_did_create,
        inode_state_will_delete,
        inode_state_did_delete,
};

static int get_cur_inode_state(struct send_ctx *sctx, u64 ino, u64 gen,
                               u64 *send_gen, u64 *parent_gen)
{
        int ret;
        int left_ret;
        int right_ret;
        u64 left_gen;
        u64 right_gen = 0;
        struct btrfs_inode_info info;

        ret = get_inode_info(sctx->send_root, ino, &info);
        if (ret < 0 && ret != -ENOENT)
                return ret;
        left_ret = (info.nlink == 0) ? -ENOENT : ret;
        left_gen = info.gen;
        if (send_gen)
                *send_gen = ((left_ret == -ENOENT) ? 0 : info.gen);

        if (!sctx->parent_root) {
                right_ret = -ENOENT;
        } else {
                ret = get_inode_info(sctx->parent_root, ino, &info);
                if (ret < 0 && ret != -ENOENT)
                        return ret;
                right_ret = (info.nlink == 0) ? -ENOENT : ret;
                right_gen = info.gen;
                if (parent_gen)
                        *parent_gen = ((right_ret == -ENOENT) ? 0 : info.gen);
        }

        if (!left_ret && !right_ret) {
                if (left_gen == gen && right_gen == gen) {
                        ret = inode_state_no_change;
                } else if (left_gen == gen) {
                        if (ino < sctx->send_progress)
                                ret = inode_state_did_create;
                        else
                                ret = inode_state_will_create;
                } else if (right_gen == gen) {
                        if (ino < sctx->send_progress)
                                ret = inode_state_did_delete;
                        else
                                ret = inode_state_will_delete;
                } else  {
                        ret = -ENOENT;
                }
        } else if (!left_ret) {
                if (left_gen == gen) {
                        if (ino < sctx->send_progress)
                                ret = inode_state_did_create;
                        else
                                ret = inode_state_will_create;
                } else {
                        ret = -ENOENT;
                }
        } else if (!right_ret) {
                if (right_gen == gen) {
                        if (ino < sctx->send_progress)
                                ret = inode_state_did_delete;
                        else
                                ret = inode_state_will_delete;
                } else {
                        ret = -ENOENT;
                }
        } else {
                ret = -ENOENT;
        }

        return ret;
}

static int is_inode_existent(struct send_ctx *sctx, u64 ino, u64 gen,
                             u64 *send_gen, u64 *parent_gen)
{
        int ret;

        if (ino == BTRFS_FIRST_FREE_OBJECTID)
                return 1;

        ret = get_cur_inode_state(sctx, ino, gen, send_gen, parent_gen);
        if (ret < 0)
                return ret;

        if (ret == inode_state_no_change ||
            ret == inode_state_did_create ||
            ret == inode_state_will_delete)
                return 1;

        return 0;
}

/*
 * Helper function to lookup a dir item in a dir.
 */
static int lookup_dir_item_inode(struct btrfs_root *root,
                                 u64 dir, const char *name, int name_len,
                                 u64 *found_inode)
{
        int ret = 0;
        struct btrfs_dir_item *di;
        struct btrfs_key key;
        BTRFS_PATH_AUTO_FREE(path);
        struct fscrypt_str name_str = FSTR_INIT((char *)name, name_len);

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        di = btrfs_lookup_dir_item(NULL, root, path, dir, &name_str, 0);
        if (IS_ERR_OR_NULL(di))
                return di ? PTR_ERR(di) : -ENOENT;

        btrfs_dir_item_key_to_cpu(path->nodes[0], di, &key);
        if (key.type == BTRFS_ROOT_ITEM_KEY)
                return -ENOENT;

        *found_inode = key.objectid;

        return ret;
}

/*
 * Looks up the first btrfs_inode_ref of a given ino. It returns the parent dir,
 * generation of the parent dir and the name of the dir entry.
 */
static int get_first_ref(struct btrfs_root *root, u64 ino,
                         u64 *dir, u64 *dir_gen, struct fs_path *name)
{
        int ret;
        struct btrfs_key key;
        struct btrfs_key found_key;
        BTRFS_PATH_AUTO_FREE(path);
        int len;
        u64 parent_dir;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = ino;
        key.type = BTRFS_INODE_REF_KEY;
        key.offset = 0;

        ret = btrfs_search_slot_for_read(root, &key, path, 1, 0);
        if (ret < 0)
                return ret;
        if (!ret)
                btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                path->slots[0]);
        if (ret || found_key.objectid != ino ||
            (found_key.type != BTRFS_INODE_REF_KEY &&
             found_key.type != BTRFS_INODE_EXTREF_KEY))
                return -ENOENT;

        if (found_key.type == BTRFS_INODE_REF_KEY) {
                struct btrfs_inode_ref *iref;
                iref = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                      struct btrfs_inode_ref);
                len = btrfs_inode_ref_name_len(path->nodes[0], iref);
                ret = fs_path_add_from_extent_buffer(name, path->nodes[0],
                                                     (unsigned long)(iref + 1),
                                                     len);
                parent_dir = found_key.offset;
        } else {
                struct btrfs_inode_extref *extref;
                extref = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                        struct btrfs_inode_extref);
                len = btrfs_inode_extref_name_len(path->nodes[0], extref);
                ret = fs_path_add_from_extent_buffer(name, path->nodes[0],
                                        (unsigned long)&extref->name, len);
                parent_dir = btrfs_inode_extref_parent(path->nodes[0], extref);
        }
        if (ret < 0)
                return ret;
        btrfs_release_path(path);

        if (dir_gen) {
                ret = get_inode_gen(root, parent_dir, dir_gen);
                if (ret < 0)
                        return ret;
        }

        *dir = parent_dir;

        return ret;
}

static int is_first_ref(struct btrfs_root *root,
                        u64 ino, u64 dir,
                        const char *name, int name_len)
{
        int ret;
        struct fs_path *tmp_name;
        u64 tmp_dir;

        tmp_name = fs_path_alloc();
        if (!tmp_name)
                return -ENOMEM;

        ret = get_first_ref(root, ino, &tmp_dir, NULL, tmp_name);
        if (ret < 0)
                goto out;

        if (dir != tmp_dir || name_len != fs_path_len(tmp_name)) {
                ret = 0;
                goto out;
        }

        ret = !memcmp(tmp_name->start, name, name_len);

out:
        fs_path_free(tmp_name);
        return ret;
}

/*
 * Used by process_recorded_refs to determine if a new ref would overwrite an
 * already existing ref. In case it detects an overwrite, it returns the
 * inode/gen in who_ino/who_gen.
 * When an overwrite is detected, process_recorded_refs does proper orphanizing
 * to make sure later references to the overwritten inode are possible.
 * Orphanizing is however only required for the first ref of an inode.
 * process_recorded_refs does an additional is_first_ref check to see if
 * orphanizing is really required.
 */
static int will_overwrite_ref(struct send_ctx *sctx, u64 dir, u64 dir_gen,
                              const char *name, int name_len,
                              u64 *who_ino, u64 *who_gen, u64 *who_mode)
{
        int ret;
        u64 parent_root_dir_gen;
        u64 other_inode = 0;
        struct btrfs_inode_info info;

        if (!sctx->parent_root)
                return 0;

        ret = is_inode_existent(sctx, dir, dir_gen, NULL, &parent_root_dir_gen);
        if (ret <= 0)
                return 0;

        /*
         * If we have a parent root we need to verify that the parent dir was
         * not deleted and then re-created, if it was then we have no overwrite
         * and we can just unlink this entry.
         *
         * @parent_root_dir_gen was set to 0 if the inode does not exist in the
         * parent root.
         */
        if (sctx->parent_root && dir != BTRFS_FIRST_FREE_OBJECTID &&
            parent_root_dir_gen != dir_gen)
                return 0;

        ret = lookup_dir_item_inode(sctx->parent_root, dir, name, name_len,
                                    &other_inode);
        if (ret == -ENOENT)
                return 0;
        else if (ret < 0)
                return ret;

        /*
         * Check if the overwritten ref was already processed. If yes, the ref
         * was already unlinked/moved, so we can safely assume that we will not
         * overwrite anything at this point in time.
         */
        if (other_inode > sctx->send_progress ||
            is_waiting_for_move(sctx, other_inode)) {
                ret = get_inode_info(sctx->parent_root, other_inode, &info);
                if (ret < 0)
                        return ret;

                *who_ino = other_inode;
                *who_gen = info.gen;
                *who_mode = info.mode;
                return 1;
        }

        return 0;
}

/*
 * Checks if the ref was overwritten by an already processed inode. This is
 * used by __get_cur_name_and_parent to find out if the ref was orphanized and
 * thus the orphan name needs be used.
 * process_recorded_refs also uses it to avoid unlinking of refs that were
 * overwritten.
 */
static int did_overwrite_ref(struct send_ctx *sctx,
                            u64 dir, u64 dir_gen,
                            u64 ino, u64 ino_gen,
                            const char *name, int name_len)
{
        int ret;
        u64 ow_inode;
        u64 ow_gen = 0;
        u64 send_root_dir_gen;

        if (!sctx->parent_root)
                return 0;

        ret = is_inode_existent(sctx, dir, dir_gen, &send_root_dir_gen, NULL);
        if (ret <= 0)
                return ret;

        /*
         * @send_root_dir_gen was set to 0 if the inode does not exist in the
         * send root.
         */
        if (dir != BTRFS_FIRST_FREE_OBJECTID && send_root_dir_gen != dir_gen)
                return 0;

        /* check if the ref was overwritten by another ref */
        ret = lookup_dir_item_inode(sctx->send_root, dir, name, name_len,
                                    &ow_inode);
        if (ret == -ENOENT) {
                /* was never and will never be overwritten */
                return 0;
        } else if (ret < 0) {
                return ret;
        }

        if (ow_inode == ino) {
                ret = get_inode_gen(sctx->send_root, ow_inode, &ow_gen);
                if (ret < 0)
                        return ret;

                /* It's the same inode, so no overwrite happened. */
                if (ow_gen == ino_gen)
                        return 0;
        }

        /*
         * We know that it is or will be overwritten. Check this now.
         * The current inode being processed might have been the one that caused
         * inode 'ino' to be orphanized, therefore check if ow_inode matches
         * the current inode being processed.
         */
        if (ow_inode < sctx->send_progress)
                return 1;

        if (ino != sctx->cur_ino && ow_inode == sctx->cur_ino) {
                if (ow_gen == 0) {
                        ret = get_inode_gen(sctx->send_root, ow_inode, &ow_gen);
                        if (ret < 0)
                                return ret;
                }
                if (ow_gen == sctx->cur_inode_gen)
                        return 1;
        }

        return 0;
}

/*
 * Same as did_overwrite_ref, but also checks if it is the first ref of an inode
 * that got overwritten. This is used by process_recorded_refs to determine
 * if it has to use the path as returned by get_cur_path or the orphan name.
 */
static int did_overwrite_first_ref(struct send_ctx *sctx, u64 ino, u64 gen)
{
        int ret = 0;
        struct fs_path *name = NULL;
        u64 dir;
        u64 dir_gen;

        if (!sctx->parent_root)
                goto out;

        name = fs_path_alloc();
        if (!name)
                return -ENOMEM;

        ret = get_first_ref(sctx->parent_root, ino, &dir, &dir_gen, name);
        if (ret < 0)
                goto out;

        ret = did_overwrite_ref(sctx, dir, dir_gen, ino, gen,
                        name->start, fs_path_len(name));

out:
        fs_path_free(name);
        return ret;
}

static inline struct name_cache_entry *name_cache_search(struct send_ctx *sctx,
                                                         u64 ino, u64 gen)
{
        struct btrfs_lru_cache_entry *entry;

        entry = btrfs_lru_cache_lookup(&sctx->name_cache, ino, gen);
        if (!entry)
                return NULL;

        return container_of(entry, struct name_cache_entry, entry);
}

/*
 * Used by get_cur_path for each ref up to the root.
 * Returns 0 if it succeeded.
 * Returns 1 if the inode is not existent or got overwritten. In that case, the
 * name is an orphan name. This instructs get_cur_path to stop iterating. If 1
 * is returned, parent_ino/parent_gen are not guaranteed to be valid.
 * Returns <0 in case of error.
 */
static int __get_cur_name_and_parent(struct send_ctx *sctx,
                                     u64 ino, u64 gen,
                                     u64 *parent_ino,
                                     u64 *parent_gen,
                                     struct fs_path *dest)
{
        int ret;
        int nce_ret;
        struct name_cache_entry *nce;

        /*
         * First check if we already did a call to this function with the same
         * ino/gen. If yes, check if the cache entry is still up-to-date. If yes
         * return the cached result.
         */
        nce = name_cache_search(sctx, ino, gen);
        if (nce) {
                if (ino < sctx->send_progress && nce->need_later_update) {
                        btrfs_lru_cache_remove(&sctx->name_cache, &nce->entry);
                        nce = NULL;
                } else {
                        *parent_ino = nce->parent_ino;
                        *parent_gen = nce->parent_gen;
                        ret = fs_path_add(dest, nce->name, nce->name_len);
                        if (ret < 0)
                                return ret;
                        return nce->ret;
                }
        }

        /*
         * If the inode is not existent yet, add the orphan name and return 1.
         * This should only happen for the parent dir that we determine in
         * record_new_ref_if_needed().
         */
        ret = is_inode_existent(sctx, ino, gen, NULL, NULL);
        if (ret < 0)
                return ret;

        if (!ret) {
                ret = gen_unique_name(sctx, ino, gen, dest);
                if (ret < 0)
                        return ret;
                ret = 1;
                goto out_cache;
        }

        /*
         * Depending on whether the inode was already processed or not, use
         * send_root or parent_root for ref lookup.
         */
        if (ino < sctx->send_progress)
                ret = get_first_ref(sctx->send_root, ino,
                                    parent_ino, parent_gen, dest);
        else
                ret = get_first_ref(sctx->parent_root, ino,
                                    parent_ino, parent_gen, dest);
        if (ret < 0)
                return ret;

        /*
         * Check if the ref was overwritten by an inode's ref that was processed
         * earlier. If yes, treat as orphan and return 1.
         */
        ret = did_overwrite_ref(sctx, *parent_ino, *parent_gen, ino, gen,
                                dest->start, fs_path_len(dest));
        if (ret < 0)
                return ret;
        if (ret) {
                fs_path_reset(dest);
                ret = gen_unique_name(sctx, ino, gen, dest);
                if (ret < 0)
                        return ret;
                ret = 1;
        }

out_cache:
        /*
         * Store the result of the lookup in the name cache.
         */
        nce = kmalloc(sizeof(*nce) + fs_path_len(dest), GFP_KERNEL);
        if (!nce)
                return -ENOMEM;

        nce->entry.key = ino;
        nce->entry.gen = gen;
        nce->parent_ino = *parent_ino;
        nce->parent_gen = *parent_gen;
        nce->name_len = fs_path_len(dest);
        nce->ret = ret;
        memcpy(nce->name, dest->start, nce->name_len);

        if (ino < sctx->send_progress)
                nce->need_later_update = 0;
        else
                nce->need_later_update = 1;

        nce_ret = btrfs_lru_cache_store(&sctx->name_cache, &nce->entry, GFP_KERNEL);
        if (nce_ret < 0) {
                kfree(nce);
                return nce_ret;
        }

        return ret;
}

/*
 * Magic happens here. This function returns the first ref to an inode as it
 * would look like while receiving the stream at this point in time.
 * We walk the path up to the root. For every inode in between, we check if it
 * was already processed/sent. If yes, we continue with the parent as found
 * in send_root. If not, we continue with the parent as found in parent_root.
 * If we encounter an inode that was deleted at this point in time, we use the
 * inodes "orphan" name instead of the real name and stop. Same with new inodes
 * that were not created yet and overwritten inodes/refs.
 *
 * When do we have orphan inodes:
 * 1. When an inode is freshly created and thus no valid refs are available yet
 * 2. When a directory lost all it's refs (deleted) but still has dir items
 *    inside which were not processed yet (pending for move/delete). If anyone
 *    tried to get the path to the dir items, it would get a path inside that
 *    orphan directory.
 * 3. When an inode is moved around or gets new links, it may overwrite the ref
 *    of an unprocessed inode. If in that case the first ref would be
 *    overwritten, the overwritten inode gets "orphanized". Later when we
 *    process this overwritten inode, it is restored at a new place by moving
 *    the orphan inode.
 *
 * sctx->send_progress tells this function at which point in time receiving
 * would be.
 */
static int get_cur_path(struct send_ctx *sctx, u64 ino, u64 gen,
                        struct fs_path *dest)
{
        int ret = 0;
        struct fs_path *name = NULL;
        u64 parent_inode = 0;
        u64 parent_gen = 0;
        int stop = 0;
        const bool is_cur_inode = (ino == sctx->cur_ino && gen == sctx->cur_inode_gen);

        if (is_cur_inode && fs_path_len(&sctx->cur_inode_path) > 0) {
                if (dest != &sctx->cur_inode_path)
                        return fs_path_copy(dest, &sctx->cur_inode_path);

                return 0;
        }

        name = fs_path_alloc();
        if (!name) {
                ret = -ENOMEM;
                goto out;
        }

        dest->reversed = 1;
        fs_path_reset(dest);

        while (!stop && ino != BTRFS_FIRST_FREE_OBJECTID) {
                struct waiting_dir_move *wdm;

                fs_path_reset(name);

                if (is_waiting_for_rm(sctx, ino, gen)) {
                        ret = gen_unique_name(sctx, ino, gen, name);
                        if (ret < 0)
                                goto out;
                        ret = fs_path_add_path(dest, name);
                        break;
                }

                wdm = get_waiting_dir_move(sctx, ino);
                if (wdm && wdm->orphanized) {
                        ret = gen_unique_name(sctx, ino, gen, name);
                        stop = 1;
                } else if (wdm) {
                        ret = get_first_ref(sctx->parent_root, ino,
                                            &parent_inode, &parent_gen, name);
                } else {
                        ret = __get_cur_name_and_parent(sctx, ino, gen,
                                                        &parent_inode,
                                                        &parent_gen, name);
                        if (ret)
                                stop = 1;
                }

                if (ret < 0)
                        goto out;

                ret = fs_path_add_path(dest, name);
                if (ret < 0)
                        goto out;

                ino = parent_inode;
                gen = parent_gen;
        }

out:
        fs_path_free(name);
        if (!ret) {
                fs_path_unreverse(dest);
                if (is_cur_inode && dest != &sctx->cur_inode_path)
                        ret = fs_path_copy(&sctx->cur_inode_path, dest);
        }

        return ret;
}

/*
 * Sends a BTRFS_SEND_C_SUBVOL command/item to userspace
 */
static int send_subvol_begin(struct send_ctx *sctx)
{
        int ret;
        struct btrfs_root *send_root = sctx->send_root;
        struct btrfs_root *parent_root = sctx->parent_root;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct btrfs_root_ref *ref;
        struct extent_buffer *leaf;
        char AUTO_KFREE(name);
        int namelen;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        name = kmalloc(BTRFS_PATH_NAME_MAX, GFP_KERNEL);
        if (!name)
                return -ENOMEM;

        key.objectid = btrfs_root_id(send_root);
        key.type = BTRFS_ROOT_BACKREF_KEY;
        key.offset = 0;

        ret = btrfs_search_slot_for_read(send_root->fs_info->tree_root,
                                &key, path, 1, 0);
        if (ret < 0)
                return ret;
        if (ret)
                return -ENOENT;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (key.type != BTRFS_ROOT_BACKREF_KEY ||
            key.objectid != btrfs_root_id(send_root)) {
                return -ENOENT;
        }
        ref = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_root_ref);
        namelen = btrfs_root_ref_name_len(leaf, ref);
        read_extent_buffer(leaf, name, (unsigned long)(ref + 1), namelen);
        btrfs_release_path(path);

        if (parent_root) {
                ret = begin_cmd(sctx, BTRFS_SEND_C_SNAPSHOT);
                if (ret < 0)
                        return ret;
        } else {
                ret = begin_cmd(sctx, BTRFS_SEND_C_SUBVOL);
                if (ret < 0)
                        return ret;
        }

        TLV_PUT_STRING(sctx, BTRFS_SEND_A_PATH, name, namelen);

        if (!btrfs_is_empty_uuid(sctx->send_root->root_item.received_uuid))
                TLV_PUT_UUID(sctx, BTRFS_SEND_A_UUID,
                            sctx->send_root->root_item.received_uuid);
        else
                TLV_PUT_UUID(sctx, BTRFS_SEND_A_UUID,
                            sctx->send_root->root_item.uuid);

        TLV_PUT_U64(sctx, BTRFS_SEND_A_CTRANSID,
                    btrfs_root_ctransid(&sctx->send_root->root_item));
        if (parent_root) {
                if (!btrfs_is_empty_uuid(parent_root->root_item.received_uuid))
                        TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                                     parent_root->root_item.received_uuid);
                else
                        TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                                     parent_root->root_item.uuid);
                TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_CTRANSID,
                            btrfs_root_ctransid(&sctx->parent_root->root_item));
        }

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

static struct fs_path *get_cur_inode_path(struct send_ctx *sctx)
{
        if (fs_path_len(&sctx->cur_inode_path) == 0) {
                int ret;

                ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                   &sctx->cur_inode_path);
                if (ret < 0)
                        return ERR_PTR(ret);
        }

        return &sctx->cur_inode_path;
}

static struct fs_path *get_path_for_command(struct send_ctx *sctx, u64 ino, u64 gen)
{
        struct fs_path *path;
        int ret;

        if (ino == sctx->cur_ino && gen == sctx->cur_inode_gen)
                return get_cur_inode_path(sctx);

        path = fs_path_alloc();
        if (!path)
                return ERR_PTR(-ENOMEM);

        ret = get_cur_path(sctx, ino, gen, path);
        if (ret < 0) {
                fs_path_free(path);
                return ERR_PTR(ret);
        }

        return path;
}

static void free_path_for_command(const struct send_ctx *sctx, struct fs_path *path)
{
        if (path != &sctx->cur_inode_path)
                fs_path_free(path);
}

static int send_truncate(struct send_ctx *sctx, u64 ino, u64 gen, u64 size)
{
        int ret = 0;
        struct fs_path *p;

        p = get_path_for_command(sctx, ino, gen);
        if (IS_ERR(p))
                return PTR_ERR(p);

        ret = begin_cmd(sctx, BTRFS_SEND_C_TRUNCATE);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_SIZE, size);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        free_path_for_command(sctx, p);
        return ret;
}

static int send_chmod(struct send_ctx *sctx, u64 ino, u64 gen, u64 mode)
{
        int ret = 0;
        struct fs_path *p;

        p = get_path_for_command(sctx, ino, gen);
        if (IS_ERR(p))
                return PTR_ERR(p);

        ret = begin_cmd(sctx, BTRFS_SEND_C_CHMOD);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_MODE, mode & 07777);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        free_path_for_command(sctx, p);
        return ret;
}

static int send_fileattr(struct send_ctx *sctx, u64 ino, u64 gen, u64 fileattr)
{
        int ret = 0;
        struct fs_path *p;

        if (sctx->proto < 2)
                return 0;

        p = get_path_for_command(sctx, ino, gen);
        if (IS_ERR(p))
                return PTR_ERR(p);

        ret = begin_cmd(sctx, BTRFS_SEND_C_FILEATTR);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILEATTR, fileattr);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        free_path_for_command(sctx, p);
        return ret;
}

static int send_chown(struct send_ctx *sctx, u64 ino, u64 gen, u64 uid, u64 gid)
{
        int ret = 0;
        struct fs_path *p;

        p = get_path_for_command(sctx, ino, gen);
        if (IS_ERR(p))
                return PTR_ERR(p);

        ret = begin_cmd(sctx, BTRFS_SEND_C_CHOWN);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_UID, uid);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_GID, gid);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        free_path_for_command(sctx, p);
        return ret;
}

static int send_utimes(struct send_ctx *sctx, u64 ino, u64 gen)
{
        int ret = 0;
        struct fs_path *p = NULL;
        struct btrfs_inode_item *ii;
        BTRFS_PATH_AUTO_FREE(path);
        struct extent_buffer *eb;
        struct btrfs_key key;
        int slot;

        p = get_path_for_command(sctx, ino, gen);
        if (IS_ERR(p))
                return PTR_ERR(p);

        path = alloc_path_for_send();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        key.objectid = ino;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;
        ret = btrfs_search_slot(NULL, sctx->send_root, &key, path, 0, 0);
        if (ret > 0)
                ret = -ENOENT;
        if (ret < 0)
                goto out;

        eb = path->nodes[0];
        slot = path->slots[0];
        ii = btrfs_item_ptr(eb, slot, struct btrfs_inode_item);

        ret = begin_cmd(sctx, BTRFS_SEND_C_UTIMES);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_ATIME, eb, &ii->atime);
        TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_MTIME, eb, &ii->mtime);
        TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_CTIME, eb, &ii->ctime);
        if (sctx->proto >= 2)
                TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_OTIME, eb, &ii->otime);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        free_path_for_command(sctx, p);
        return ret;
}

/*
 * If the cache is full, we can't remove entries from it and do a call to
 * send_utimes() for each respective inode, because we might be finishing
 * processing an inode that is a directory and it just got renamed, and existing
 * entries in the cache may refer to inodes that have the directory in their
 * full path - in which case we would generate outdated paths (pre-rename)
 * for the inodes that the cache entries point to. Instead of pruning the
 * cache when inserting, do it after we finish processing each inode at
 * finish_inode_if_needed().
 */
static int cache_dir_utimes(struct send_ctx *sctx, u64 dir, u64 gen)
{
        struct btrfs_lru_cache_entry *entry;
        int ret;

        entry = btrfs_lru_cache_lookup(&sctx->dir_utimes_cache, dir, gen);
        if (entry != NULL)
                return 0;

        /* Caching is optional, don't fail if we can't allocate memory. */
        entry = kmalloc_obj(*entry);
        if (!entry)
                return send_utimes(sctx, dir, gen);

        entry->key = dir;
        entry->gen = gen;

        ret = btrfs_lru_cache_store(&sctx->dir_utimes_cache, entry, GFP_KERNEL);
        ASSERT(ret != -EEXIST);
        if (ret) {
                kfree(entry);
                return send_utimes(sctx, dir, gen);
        }

        return 0;
}

static int trim_dir_utimes_cache(struct send_ctx *sctx)
{
        while (sctx->dir_utimes_cache.size > SEND_MAX_DIR_UTIMES_CACHE_SIZE) {
                struct btrfs_lru_cache_entry *lru;
                int ret;

                lru = btrfs_lru_cache_lru_entry(&sctx->dir_utimes_cache);
                ASSERT(lru != NULL);

                ret = send_utimes(sctx, lru->key, lru->gen);
                if (ret)
                        return ret;

                btrfs_lru_cache_remove(&sctx->dir_utimes_cache, lru);
        }

        return 0;
}

/*
 * Sends a BTRFS_SEND_C_MKXXX or SYMLINK command to user space. We don't have
 * a valid path yet because we did not process the refs yet. So, the inode
 * is created as orphan.
 */
static int send_create_inode(struct send_ctx *sctx, u64 ino)
{
        int ret = 0;
        struct fs_path *p;
        int cmd;
        struct btrfs_inode_info info;
        u64 gen;
        u64 mode;
        u64 rdev;

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        if (ino != sctx->cur_ino) {
                ret = get_inode_info(sctx->send_root, ino, &info);
                if (ret < 0)
                        goto out;
                gen = info.gen;
                mode = info.mode;
                rdev = info.rdev;
        } else {
                gen = sctx->cur_inode_gen;
                mode = sctx->cur_inode_mode;
                rdev = sctx->cur_inode_rdev;
        }

        if (S_ISREG(mode)) {
                cmd = BTRFS_SEND_C_MKFILE;
        } else if (S_ISDIR(mode)) {
                cmd = BTRFS_SEND_C_MKDIR;
        } else if (S_ISLNK(mode)) {
                cmd = BTRFS_SEND_C_SYMLINK;
        } else if (S_ISCHR(mode) || S_ISBLK(mode)) {
                cmd = BTRFS_SEND_C_MKNOD;
        } else if (S_ISFIFO(mode)) {
                cmd = BTRFS_SEND_C_MKFIFO;
        } else if (S_ISSOCK(mode)) {
                cmd = BTRFS_SEND_C_MKSOCK;
        } else {
                btrfs_warn(sctx->send_root->fs_info, "unexpected inode type %o",
                                (int)(mode & S_IFMT));
                ret = -EOPNOTSUPP;
                goto out;
        }

        ret = begin_cmd(sctx, cmd);
        if (ret < 0)
                goto out;

        ret = gen_unique_name(sctx, ino, gen, p);
        if (ret < 0)
                goto out;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_INO, ino);

        if (S_ISLNK(mode)) {
                fs_path_reset(p);
                ret = read_symlink(sctx->send_root, ino, p);
                if (ret < 0)
                        goto out;
                TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_LINK, p);
        } else if (S_ISCHR(mode) || S_ISBLK(mode) ||
                   S_ISFIFO(mode) || S_ISSOCK(mode)) {
                TLV_PUT_U64(sctx, BTRFS_SEND_A_RDEV, new_encode_dev(rdev));
                TLV_PUT_U64(sctx, BTRFS_SEND_A_MODE, mode);
        }

        ret = send_cmd(sctx);
        if (ret < 0)
                goto out;


tlv_put_failure:
out:
        fs_path_free(p);
        return ret;
}

static void cache_dir_created(struct send_ctx *sctx, u64 dir)
{
        struct btrfs_lru_cache_entry *entry;
        int ret;

        /* Caching is optional, ignore any failures. */
        entry = kmalloc_obj(*entry);
        if (!entry)
                return;

        entry->key = dir;
        entry->gen = 0;
        ret = btrfs_lru_cache_store(&sctx->dir_created_cache, entry, GFP_KERNEL);
        if (ret < 0)
                kfree(entry);
}

/*
 * We need some special handling for inodes that get processed before the parent
 * directory got created. See process_recorded_refs for details.
 * This function does the check if we already created the dir out of order.
 */
static int did_create_dir(struct send_ctx *sctx, u64 dir)
{
        int ret = 0;
        int iter_ret = 0;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_key di_key;
        struct btrfs_dir_item *di;

        if (btrfs_lru_cache_lookup(&sctx->dir_created_cache, dir, 0))
                return 1;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = dir;
        key.type = BTRFS_DIR_INDEX_KEY;
        key.offset = 0;

        btrfs_for_each_slot(sctx->send_root, &key, &found_key, path, iter_ret) {
                struct extent_buffer *eb = path->nodes[0];

                if (found_key.objectid != key.objectid ||
                    found_key.type != key.type) {
                        ret = 0;
                        break;
                }

                di = btrfs_item_ptr(eb, path->slots[0], struct btrfs_dir_item);
                btrfs_dir_item_key_to_cpu(eb, di, &di_key);

                if (di_key.type != BTRFS_ROOT_ITEM_KEY &&
                    di_key.objectid < sctx->send_progress) {
                        ret = 1;
                        cache_dir_created(sctx, dir);
                        break;
                }
        }
        /* Catch error found during iteration */
        if (iter_ret < 0)
                ret = iter_ret;

        return ret;
}

/*
 * Only creates the inode if it is:
 * 1. Not a directory
 * 2. Or a directory which was not created already due to out of order
 *    directories. See did_create_dir and process_recorded_refs for details.
 */
static int send_create_inode_if_needed(struct send_ctx *sctx)
{
        int ret;

        if (S_ISDIR(sctx->cur_inode_mode)) {
                ret = did_create_dir(sctx, sctx->cur_ino);
                if (ret < 0)
                        return ret;
                else if (ret > 0)
                        return 0;
        }

        ret = send_create_inode(sctx, sctx->cur_ino);

        if (ret == 0 && S_ISDIR(sctx->cur_inode_mode))
                cache_dir_created(sctx, sctx->cur_ino);

        return ret;
}

struct recorded_ref {
        struct list_head list;
        char *name;
        struct fs_path *full_path;
        u64 dir;
        u64 dir_gen;
        int name_len;
        struct rb_node node;
        struct rb_root *root;
};

static struct recorded_ref *recorded_ref_alloc(void)
{
        struct recorded_ref *ref;

        ref = kzalloc_obj(*ref);
        if (!ref)
                return NULL;
        RB_CLEAR_NODE(&ref->node);
        INIT_LIST_HEAD(&ref->list);
        return ref;
}

static void recorded_ref_free(struct recorded_ref *ref)
{
        if (!ref)
                return;
        if (!RB_EMPTY_NODE(&ref->node))
                rb_erase(&ref->node, ref->root);
        list_del(&ref->list);
        fs_path_free(ref->full_path);
        kfree(ref);
}

static void set_ref_path(struct recorded_ref *ref, struct fs_path *path)
{
        ref->full_path = path;
        ref->name = (char *)kbasename(ref->full_path->start);
        ref->name_len = ref->full_path->end - ref->name;
}

static int dup_ref(struct recorded_ref *ref, struct list_head *list)
{
        struct recorded_ref *new;

        new = recorded_ref_alloc();
        if (!new)
                return -ENOMEM;

        new->dir = ref->dir;
        new->dir_gen = ref->dir_gen;
        list_add_tail(&new->list, list);
        return 0;
}

static void __free_recorded_refs(struct list_head *head)
{
        struct recorded_ref *cur;

        while (!list_empty(head)) {
                cur = list_first_entry(head, struct recorded_ref, list);
                recorded_ref_free(cur);
        }
}

static void free_recorded_refs(struct send_ctx *sctx)
{
        __free_recorded_refs(&sctx->new_refs);
        __free_recorded_refs(&sctx->deleted_refs);
}

/*
 * Renames/moves a file/dir to its orphan name. Used when the first
 * ref of an unprocessed inode gets overwritten and for all non empty
 * directories.
 */
static int orphanize_inode(struct send_ctx *sctx, u64 ino, u64 gen,
                          struct fs_path *path)
{
        int ret;
        struct fs_path *orphan;

        orphan = fs_path_alloc();
        if (!orphan)
                return -ENOMEM;

        ret = gen_unique_name(sctx, ino, gen, orphan);
        if (ret < 0)
                goto out;

        ret = send_rename(sctx, path, orphan);
        if (ret < 0)
                goto out;

        if (ino == sctx->cur_ino && gen == sctx->cur_inode_gen)
                ret = fs_path_copy(&sctx->cur_inode_path, orphan);

out:
        fs_path_free(orphan);
        return ret;
}

static struct orphan_dir_info *add_orphan_dir_info(struct send_ctx *sctx,
                                                   u64 dir_ino, u64 dir_gen)
{
        struct rb_node **p = &sctx->orphan_dirs.rb_node;
        struct rb_node *parent = NULL;
        struct orphan_dir_info *entry, *odi;

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct orphan_dir_info, node);
                if (dir_ino < entry->ino)
                        p = &(*p)->rb_left;
                else if (dir_ino > entry->ino)
                        p = &(*p)->rb_right;
                else if (dir_gen < entry->gen)
                        p = &(*p)->rb_left;
                else if (dir_gen > entry->gen)
                        p = &(*p)->rb_right;
                else
                        return entry;
        }

        odi = kmalloc_obj(*odi);
        if (!odi)
                return ERR_PTR(-ENOMEM);
        odi->ino = dir_ino;
        odi->gen = dir_gen;
        odi->last_dir_index_offset = 0;
        odi->dir_high_seq_ino = 0;

        rb_link_node(&odi->node, parent, p);
        rb_insert_color(&odi->node, &sctx->orphan_dirs);
        return odi;
}

static struct orphan_dir_info *get_orphan_dir_info(struct send_ctx *sctx,
                                                   u64 dir_ino, u64 gen)
{
        struct rb_node *n = sctx->orphan_dirs.rb_node;
        struct orphan_dir_info *entry;

        while (n) {
                entry = rb_entry(n, struct orphan_dir_info, node);
                if (dir_ino < entry->ino)
                        n = n->rb_left;
                else if (dir_ino > entry->ino)
                        n = n->rb_right;
                else if (gen < entry->gen)
                        n = n->rb_left;
                else if (gen > entry->gen)
                        n = n->rb_right;
                else
                        return entry;
        }
        return NULL;
}

static int is_waiting_for_rm(struct send_ctx *sctx, u64 dir_ino, u64 gen)
{
        struct orphan_dir_info *odi = get_orphan_dir_info(sctx, dir_ino, gen);

        return odi != NULL;
}

static void free_orphan_dir_info(struct send_ctx *sctx,
                                 struct orphan_dir_info *odi)
{
        if (!odi)
                return;
        rb_erase(&odi->node, &sctx->orphan_dirs);
        kfree(odi);
}

/*
 * Returns 1 if a directory can be removed at this point in time.
 * We check this by iterating all dir items and checking if the inode behind
 * the dir item was already processed.
 */
static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 dir_gen)
{
        int ret = 0;
        int iter_ret = 0;
        struct btrfs_root *root = sctx->parent_root;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_key loc;
        struct btrfs_dir_item *di;
        struct orphan_dir_info *odi = NULL;
        u64 dir_high_seq_ino = 0;
        u64 last_dir_index_offset = 0;

        /*
         * Don't try to rmdir the top/root subvolume dir.
         */
        if (dir == BTRFS_FIRST_FREE_OBJECTID)
                return 0;

        odi = get_orphan_dir_info(sctx, dir, dir_gen);
        if (odi && sctx->cur_ino < odi->dir_high_seq_ino)
                return 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        if (!odi) {
                /*
                 * Find the inode number associated with the last dir index
                 * entry. This is very likely the inode with the highest number
                 * of all inodes that have an entry in the directory. We can
                 * then use it to avoid future calls to can_rmdir(), when
                 * processing inodes with a lower number, from having to search
                 * the parent root b+tree for dir index keys.
                 */
                key.objectid = dir;
                key.type = BTRFS_DIR_INDEX_KEY;
                key.offset = (u64)-1;

                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                if (ret < 0) {
                        goto out;
                } else if (ret > 0) {
                        /* Can't happen, the root is never empty. */
                        ASSERT(path->slots[0] > 0);
                        if (WARN_ON(path->slots[0] == 0)) {
                                ret = -EUCLEAN;
                                goto out;
                        }
                        path->slots[0]--;
                }

                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
                if (key.objectid != dir || key.type != BTRFS_DIR_INDEX_KEY) {
                        /* No index keys, dir can be removed. */
                        ret = 1;
                        goto out;
                }

                di = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                    struct btrfs_dir_item);
                btrfs_dir_item_key_to_cpu(path->nodes[0], di, &loc);
                dir_high_seq_ino = loc.objectid;
                if (sctx->cur_ino < dir_high_seq_ino) {
                        ret = 0;
                        goto out;
                }

                btrfs_release_path(path);
        }

        key.objectid = dir;
        key.type = BTRFS_DIR_INDEX_KEY;
        key.offset = (odi ? odi->last_dir_index_offset : 0);

        btrfs_for_each_slot(root, &key, &found_key, path, iter_ret) {
                struct waiting_dir_move *dm;

                if (found_key.objectid != key.objectid ||
                    found_key.type != key.type)
                        break;

                di = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                struct btrfs_dir_item);
                btrfs_dir_item_key_to_cpu(path->nodes[0], di, &loc);

                dir_high_seq_ino = max(dir_high_seq_ino, loc.objectid);
                last_dir_index_offset = found_key.offset;

                dm = get_waiting_dir_move(sctx, loc.objectid);
                if (dm) {
                        dm->rmdir_ino = dir;
                        dm->rmdir_gen = dir_gen;
                        ret = 0;
                        goto out;
                }

                if (loc.objectid > sctx->cur_ino) {
                        ret = 0;
                        goto out;
                }
        }
        if (iter_ret < 0) {
                ret = iter_ret;
                goto out;
        }
        free_orphan_dir_info(sctx, odi);

        ret = 1;

out:
        btrfs_free_path(path);

        if (ret)
                return ret;

        if (!odi) {
                odi = add_orphan_dir_info(sctx, dir, dir_gen);
                if (IS_ERR(odi))
                        return PTR_ERR(odi);

                odi->gen = dir_gen;
        }

        odi->last_dir_index_offset = last_dir_index_offset;
        odi->dir_high_seq_ino = max(odi->dir_high_seq_ino, dir_high_seq_ino);

        return 0;
}

static int is_waiting_for_move(struct send_ctx *sctx, u64 ino)
{
        struct waiting_dir_move *entry = get_waiting_dir_move(sctx, ino);

        return entry != NULL;
}

static int add_waiting_dir_move(struct send_ctx *sctx, u64 ino, bool orphanized)
{
        struct rb_node **p = &sctx->waiting_dir_moves.rb_node;
        struct rb_node *parent = NULL;
        struct waiting_dir_move *entry, *dm;

        dm = kmalloc_obj(*dm);
        if (!dm)
                return -ENOMEM;
        dm->ino = ino;
        dm->rmdir_ino = 0;
        dm->rmdir_gen = 0;
        dm->orphanized = orphanized;

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct waiting_dir_move, node);
                if (ino < entry->ino) {
                        p = &(*p)->rb_left;
                } else if (ino > entry->ino) {
                        p = &(*p)->rb_right;
                } else {
                        kfree(dm);
                        return -EEXIST;
                }
        }

        rb_link_node(&dm->node, parent, p);
        rb_insert_color(&dm->node, &sctx->waiting_dir_moves);
        return 0;
}

static struct waiting_dir_move *
get_waiting_dir_move(struct send_ctx *sctx, u64 ino)
{
        struct rb_node *n = sctx->waiting_dir_moves.rb_node;
        struct waiting_dir_move *entry;

        while (n) {
                entry = rb_entry(n, struct waiting_dir_move, node);
                if (ino < entry->ino)
                        n = n->rb_left;
                else if (ino > entry->ino)
                        n = n->rb_right;
                else
                        return entry;
        }
        return NULL;
}

static void free_waiting_dir_move(struct send_ctx *sctx,
                                  struct waiting_dir_move *dm)
{
        if (!dm)
                return;
        rb_erase(&dm->node, &sctx->waiting_dir_moves);
        kfree(dm);
}

static int add_pending_dir_move(struct send_ctx *sctx,
                                u64 ino,
                                u64 ino_gen,
                                u64 parent_ino,
                                struct list_head *new_refs,
                                struct list_head *deleted_refs,
                                const bool is_orphan)
{
        struct rb_node **p = &sctx->pending_dir_moves.rb_node;
        struct rb_node *parent = NULL;
        struct pending_dir_move *entry = NULL, *pm;
        struct recorded_ref *cur;
        int exists = 0;
        int ret;

        pm = kmalloc_obj(*pm);
        if (!pm)
                return -ENOMEM;
        pm->parent_ino = parent_ino;
        pm->ino = ino;
        pm->gen = ino_gen;
        INIT_LIST_HEAD(&pm->list);
        INIT_LIST_HEAD(&pm->update_refs);
        RB_CLEAR_NODE(&pm->node);

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct pending_dir_move, node);
                if (parent_ino < entry->parent_ino) {
                        p = &(*p)->rb_left;
                } else if (parent_ino > entry->parent_ino) {
                        p = &(*p)->rb_right;
                } else {
                        exists = 1;
                        break;
                }
        }

        list_for_each_entry(cur, deleted_refs, list) {
                ret = dup_ref(cur, &pm->update_refs);
                if (ret < 0)
                        goto out;
        }
        list_for_each_entry(cur, new_refs, list) {
                ret = dup_ref(cur, &pm->update_refs);
                if (ret < 0)
                        goto out;
        }

        ret = add_waiting_dir_move(sctx, pm->ino, is_orphan);
        if (ret)
                goto out;

        if (exists) {
                list_add_tail(&pm->list, &entry->list);
        } else {
                rb_link_node(&pm->node, parent, p);
                rb_insert_color(&pm->node, &sctx->pending_dir_moves);
        }
        ret = 0;
out:
        if (ret) {
                __free_recorded_refs(&pm->update_refs);
                kfree(pm);
        }
        return ret;
}

static struct pending_dir_move *get_pending_dir_moves(struct send_ctx *sctx,
                                                      u64 parent_ino)
{
        struct rb_node *n = sctx->pending_dir_moves.rb_node;
        struct pending_dir_move *entry;

        while (n) {
                entry = rb_entry(n, struct pending_dir_move, node);
                if (parent_ino < entry->parent_ino)
                        n = n->rb_left;
                else if (parent_ino > entry->parent_ino)
                        n = n->rb_right;
                else
                        return entry;
        }
        return NULL;
}

static int path_loop(struct send_ctx *sctx, struct fs_path *name,
                     u64 ino, u64 gen, u64 *ancestor_ino)
{
        int ret = 0;
        u64 parent_inode = 0;
        u64 parent_gen = 0;
        u64 start_ino = ino;

        *ancestor_ino = 0;
        while (ino != BTRFS_FIRST_FREE_OBJECTID) {
                fs_path_reset(name);

                if (is_waiting_for_rm(sctx, ino, gen))
                        break;
                if (is_waiting_for_move(sctx, ino)) {
                        if (*ancestor_ino == 0)
                                *ancestor_ino = ino;
                        ret = get_first_ref(sctx->parent_root, ino,
                                            &parent_inode, &parent_gen, name);
                } else {
                        ret = __get_cur_name_and_parent(sctx, ino, gen,
                                                        &parent_inode,
                                                        &parent_gen, name);
                        if (ret > 0) {
                                ret = 0;
                                break;
                        }
                }
                if (ret < 0)
                        break;
                if (parent_inode == start_ino) {
                        ret = 1;
                        if (*ancestor_ino == 0)
                                *ancestor_ino = ino;
                        break;
                }
                ino = parent_inode;
                gen = parent_gen;
        }
        return ret;
}

static int apply_dir_move(struct send_ctx *sctx, struct pending_dir_move *pm)
{
        struct fs_path *from_path = NULL;
        struct fs_path *to_path = NULL;
        struct fs_path *name = NULL;
        u64 orig_progress = sctx->send_progress;
        struct recorded_ref *cur;
        u64 parent_ino, parent_gen;
        struct waiting_dir_move *dm = NULL;
        u64 rmdir_ino = 0;
        u64 rmdir_gen;
        u64 ancestor;
        bool is_orphan;
        int ret;

        name = fs_path_alloc();
        from_path = fs_path_alloc();
        if (!name || !from_path) {
                ret = -ENOMEM;
                goto out;
        }

        dm = get_waiting_dir_move(sctx, pm->ino);
        ASSERT(dm);
        rmdir_ino = dm->rmdir_ino;
        rmdir_gen = dm->rmdir_gen;
        is_orphan = dm->orphanized;
        free_waiting_dir_move(sctx, dm);

        if (is_orphan) {
                ret = gen_unique_name(sctx, pm->ino,
                                      pm->gen, from_path);
        } else {
                ret = get_first_ref(sctx->parent_root, pm->ino,
                                    &parent_ino, &parent_gen, name);
                if (ret < 0)
                        goto out;
                ret = get_cur_path(sctx, parent_ino, parent_gen,
                                   from_path);
                if (ret < 0)
                        goto out;
                ret = fs_path_add_path(from_path, name);
        }
        if (ret < 0)
                goto out;

        sctx->send_progress = sctx->cur_ino + 1;
        ret = path_loop(sctx, name, pm->ino, pm->gen, &ancestor);
        if (ret < 0)
                goto out;
        if (ret) {
                LIST_HEAD(deleted_refs);
                ASSERT(ancestor > BTRFS_FIRST_FREE_OBJECTID);
                ret = add_pending_dir_move(sctx, pm->ino, pm->gen, ancestor,
                                           &pm->update_refs, &deleted_refs,
                                           is_orphan);
                if (ret < 0)
                        goto out;
                if (rmdir_ino) {
                        dm = get_waiting_dir_move(sctx, pm->ino);
                        ASSERT(dm);
                        dm->rmdir_ino = rmdir_ino;
                        dm->rmdir_gen = rmdir_gen;
                }
                goto out;
        }
        fs_path_reset(name);
        to_path = name;
        name = NULL;
        ret = get_cur_path(sctx, pm->ino, pm->gen, to_path);
        if (ret < 0)
                goto out;

        ret = send_rename(sctx, from_path, to_path);
        if (ret < 0)
                goto out;

        if (rmdir_ino) {
                struct orphan_dir_info *odi;
                u64 gen;

                odi = get_orphan_dir_info(sctx, rmdir_ino, rmdir_gen);
                if (!odi) {
                        /* already deleted */
                        goto finish;
                }
                gen = odi->gen;

                ret = can_rmdir(sctx, rmdir_ino, gen);
                if (ret < 0)
                        goto out;
                if (!ret)
                        goto finish;

                name = fs_path_alloc();
                if (!name) {
                        ret = -ENOMEM;
                        goto out;
                }
                ret = get_cur_path(sctx, rmdir_ino, gen, name);
                if (ret < 0)
                        goto out;
                ret = send_rmdir(sctx, name);
                if (ret < 0)
                        goto out;
        }

finish:
        ret = cache_dir_utimes(sctx, pm->ino, pm->gen);
        if (ret < 0)
                goto out;

        /*
         * After rename/move, need to update the utimes of both new parent(s)
         * and old parent(s).
         */
        list_for_each_entry(cur, &pm->update_refs, list) {
                /*
                 * The parent inode might have been deleted in the send snapshot
                 */
                ret = get_inode_info(sctx->send_root, cur->dir, NULL);
                if (ret == -ENOENT) {
                        ret = 0;
                        continue;
                }
                if (ret < 0)
                        goto out;

                ret = cache_dir_utimes(sctx, cur->dir, cur->dir_gen);
                if (ret < 0)
                        goto out;
        }

out:
        fs_path_free(name);
        fs_path_free(from_path);
        fs_path_free(to_path);
        sctx->send_progress = orig_progress;

        return ret;
}

static void free_pending_move(struct send_ctx *sctx, struct pending_dir_move *m)
{
        if (!list_empty(&m->list))
                list_del(&m->list);
        if (!RB_EMPTY_NODE(&m->node))
                rb_erase(&m->node, &sctx->pending_dir_moves);
        __free_recorded_refs(&m->update_refs);
        kfree(m);
}

static void tail_append_pending_moves(struct send_ctx *sctx,
                                      struct pending_dir_move *moves,
                                      struct list_head *stack)
{
        if (list_empty(&moves->list)) {
                list_add_tail(&moves->list, stack);
        } else {
                LIST_HEAD(list);
                list_splice_init(&moves->list, &list);
                list_add_tail(&moves->list, stack);
                list_splice_tail(&list, stack);
        }
        if (!RB_EMPTY_NODE(&moves->node)) {
                rb_erase(&moves->node, &sctx->pending_dir_moves);
                RB_CLEAR_NODE(&moves->node);
        }
}

static int apply_children_dir_moves(struct send_ctx *sctx)
{
        struct pending_dir_move *pm;
        LIST_HEAD(stack);
        u64 parent_ino = sctx->cur_ino;
        int ret = 0;

        pm = get_pending_dir_moves(sctx, parent_ino);
        if (!pm)
                return 0;

        tail_append_pending_moves(sctx, pm, &stack);

        while (!list_empty(&stack)) {
                pm = list_first_entry(&stack, struct pending_dir_move, list);
                parent_ino = pm->ino;
                ret = apply_dir_move(sctx, pm);
                free_pending_move(sctx, pm);
                if (ret)
                        goto out;
                pm = get_pending_dir_moves(sctx, parent_ino);
                if (pm)
                        tail_append_pending_moves(sctx, pm, &stack);
        }
        return 0;

out:
        while (!list_empty(&stack)) {
                pm = list_first_entry(&stack, struct pending_dir_move, list);
                free_pending_move(sctx, pm);
        }
        return ret;
}

/*
 * We might need to delay a directory rename even when no ancestor directory
 * (in the send root) with a higher inode number than ours (sctx->cur_ino) was
 * renamed. This happens when we rename a directory to the old name (the name
 * in the parent root) of some other unrelated directory that got its rename
 * delayed due to some ancestor with higher number that got renamed.
 *
 * Example:
 *
 * Parent snapshot:
 * .                                       (ino 256)
 * |---- a/                                (ino 257)
 * |     |---- file                        (ino 260)
 * |
 * |---- b/                                (ino 258)
 * |---- c/                                (ino 259)
 *
 * Send snapshot:
 * .                                       (ino 256)
 * |---- a/                                (ino 258)
 * |---- x/                                (ino 259)
 *       |---- y/                          (ino 257)
 *             |----- file                 (ino 260)
 *
 * Here we can not rename 258 from 'b' to 'a' without the rename of inode 257
 * from 'a' to 'x/y' happening first, which in turn depends on the rename of
 * inode 259 from 'c' to 'x'. So the order of rename commands the send stream
 * must issue is:
 *
 * 1 - rename 259 from 'c' to 'x'
 * 2 - rename 257 from 'a' to 'x/y'
 * 3 - rename 258 from 'b' to 'a'
 *
 * Returns 1 if the rename of sctx->cur_ino needs to be delayed, 0 if it can
 * be done right away and < 0 on error.
 */
static int wait_for_dest_dir_move(struct send_ctx *sctx,
                                  struct recorded_ref *parent_ref,
                                  const bool is_orphan)
{
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct btrfs_key di_key;
        struct btrfs_dir_item *di;
        u64 left_gen;
        u64 right_gen;
        int ret = 0;
        struct waiting_dir_move *wdm;

        if (RB_EMPTY_ROOT(&sctx->waiting_dir_moves))
                return 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = parent_ref->dir;
        key.type = BTRFS_DIR_ITEM_KEY;
        key.offset = btrfs_name_hash(parent_ref->name, parent_ref->name_len);

        ret = btrfs_search_slot(NULL, sctx->parent_root, &key, path, 0, 0);
        if (ret < 0)
                return ret;
        if (ret > 0)
                return 0;

        di = btrfs_match_dir_item_name(path, parent_ref->name,
                                       parent_ref->name_len);
        if (!di)
                return 0;
        /*
         * di_key.objectid has the number of the inode that has a dentry in the
         * parent directory with the same name that sctx->cur_ino is being
         * renamed to. We need to check if that inode is in the send root as
         * well and if it is currently marked as an inode with a pending rename,
         * if it is, we need to delay the rename of sctx->cur_ino as well, so
         * that it happens after that other inode is renamed.
         */
        btrfs_dir_item_key_to_cpu(path->nodes[0], di, &di_key);
        if (di_key.type != BTRFS_INODE_ITEM_KEY)
                return 0;

        ret = get_inode_gen(sctx->parent_root, di_key.objectid, &left_gen);
        if (ret < 0)
                return ret;
        ret = get_inode_gen(sctx->send_root, di_key.objectid, &right_gen);
        if (ret < 0) {
                if (ret == -ENOENT)
                        ret = 0;
                return ret;
        }

        /* Different inode, no need to delay the rename of sctx->cur_ino */
        if (right_gen != left_gen)
                return 0;

        wdm = get_waiting_dir_move(sctx, di_key.objectid);
        if (wdm && !wdm->orphanized) {
                ret = add_pending_dir_move(sctx,
                                           sctx->cur_ino,
                                           sctx->cur_inode_gen,
                                           di_key.objectid,
                                           &sctx->new_refs,
                                           &sctx->deleted_refs,
                                           is_orphan);
                if (!ret)
                        ret = 1;
        }
        return ret;
}

/*
 * Check if inode ino2, or any of its ancestors, is inode ino1.
 * Return 1 if true, 0 if false and < 0 on error.
 */
static int check_ino_in_path(struct btrfs_root *root,
                             const u64 ino1,
                             const u64 ino1_gen,
                             const u64 ino2,
                             const u64 ino2_gen,
                             struct fs_path *fs_path)
{
        u64 ino = ino2;

        if (ino1 == ino2)
                return ino1_gen == ino2_gen;

        while (ino > BTRFS_FIRST_FREE_OBJECTID) {
                u64 parent;
                u64 parent_gen;
                int ret;

                fs_path_reset(fs_path);
                ret = get_first_ref(root, ino, &parent, &parent_gen, fs_path);
                if (ret < 0)
                        return ret;
                if (parent == ino1)
                        return parent_gen == ino1_gen;
                ino = parent;
        }
        return 0;
}

/*
 * Check if inode ino1 is an ancestor of inode ino2 in the given root for any
 * possible path (in case ino2 is not a directory and has multiple hard links).
 * Return 1 if true, 0 if false and < 0 on error.
 */
static int is_ancestor(struct btrfs_root *root,
                       const u64 ino1,
                       const u64 ino1_gen,
                       const u64 ino2,
                       struct fs_path *fs_path)
{
        bool free_fs_path = false;
        int ret = 0;
        int iter_ret = 0;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;

        if (!fs_path) {
                fs_path = fs_path_alloc();
                if (!fs_path)
                        return -ENOMEM;
                free_fs_path = true;
        }

        path = alloc_path_for_send();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        key.objectid = ino2;
        key.type = BTRFS_INODE_REF_KEY;
        key.offset = 0;

        btrfs_for_each_slot(root, &key, &key, path, iter_ret) {
                struct extent_buffer *leaf = path->nodes[0];
                int slot = path->slots[0];
                u32 cur_offset = 0;
                u32 item_size;

                if (key.objectid != ino2)
                        break;
                if (key.type != BTRFS_INODE_REF_KEY &&
                    key.type != BTRFS_INODE_EXTREF_KEY)
                        break;

                item_size = btrfs_item_size(leaf, slot);
                while (cur_offset < item_size) {
                        u64 parent;
                        u64 parent_gen;

                        if (key.type == BTRFS_INODE_EXTREF_KEY) {
                                unsigned long ptr;
                                struct btrfs_inode_extref *extref;

                                ptr = btrfs_item_ptr_offset(leaf, slot);
                                extref = (struct btrfs_inode_extref *)
                                        (ptr + cur_offset);
                                parent = btrfs_inode_extref_parent(leaf,
                                                                   extref);
                                cur_offset += sizeof(*extref);
                                cur_offset += btrfs_inode_extref_name_len(leaf,
                                                                  extref);
                        } else {
                                parent = key.offset;
                                cur_offset = item_size;
                        }

                        ret = get_inode_gen(root, parent, &parent_gen);
                        if (ret < 0)
                                goto out;
                        ret = check_ino_in_path(root, ino1, ino1_gen,
                                                parent, parent_gen, fs_path);
                        if (ret)
                                goto out;
                }
        }
        ret = 0;
        if (iter_ret < 0)
                ret = iter_ret;

out:
        if (free_fs_path)
                fs_path_free(fs_path);
        return ret;
}

static int wait_for_parent_move(struct send_ctx *sctx,
                                struct recorded_ref *parent_ref,
                                const bool is_orphan)
{
        int ret = 0;
        u64 ino = parent_ref->dir;
        u64 ino_gen = parent_ref->dir_gen;
        u64 parent_ino_before, parent_ino_after;
        struct fs_path *path_before = NULL;
        struct fs_path *path_after = NULL;
        int len1, len2;

        path_after = fs_path_alloc();
        path_before = fs_path_alloc();
        if (!path_after || !path_before) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * Our current directory inode may not yet be renamed/moved because some
         * ancestor (immediate or not) has to be renamed/moved first. So find if
         * such ancestor exists and make sure our own rename/move happens after
         * that ancestor is processed to avoid path build infinite loops (done
         * at get_cur_path()).
         */
        while (ino > BTRFS_FIRST_FREE_OBJECTID) {
                u64 parent_ino_after_gen;

                if (is_waiting_for_move(sctx, ino)) {
                        /*
                         * If the current inode is an ancestor of ino in the
                         * parent root, we need to delay the rename of the
                         * current inode, otherwise don't delayed the rename
                         * because we can end up with a circular dependency
                         * of renames, resulting in some directories never
                         * getting the respective rename operations issued in
                         * the send stream or getting into infinite path build
                         * loops.
                         */
                        ret = is_ancestor(sctx->parent_root,
                                          sctx->cur_ino, sctx->cur_inode_gen,
                                          ino, path_before);
                        if (ret)
                                break;
                }

                fs_path_reset(path_before);
                fs_path_reset(path_after);

                ret = get_first_ref(sctx->send_root, ino, &parent_ino_after,
                                    &parent_ino_after_gen, path_after);
                if (ret < 0)
                        goto out;
                ret = get_first_ref(sctx->parent_root, ino, &parent_ino_before,
                                    NULL, path_before);
                if (ret < 0 && ret != -ENOENT) {
                        goto out;
                } else if (ret == -ENOENT) {
                        ret = 0;
                        break;
                }

                len1 = fs_path_len(path_before);
                len2 = fs_path_len(path_after);
                if (ino > sctx->cur_ino &&
                    (parent_ino_before != parent_ino_after || len1 != len2 ||
                     memcmp(path_before->start, path_after->start, len1))) {
                        u64 parent_ino_gen;

                        ret = get_inode_gen(sctx->parent_root, ino, &parent_ino_gen);
                        if (ret < 0)
                                goto out;
                        if (ino_gen == parent_ino_gen) {
                                ret = 1;
                                break;
                        }
                }
                ino = parent_ino_after;
                ino_gen = parent_ino_after_gen;
        }

out:
        fs_path_free(path_before);
        fs_path_free(path_after);

        if (ret == 1) {
                ret = add_pending_dir_move(sctx,
                                           sctx->cur_ino,
                                           sctx->cur_inode_gen,
                                           ino,
                                           &sctx->new_refs,
                                           &sctx->deleted_refs,
                                           is_orphan);
                if (!ret)
                        ret = 1;
        }

        return ret;
}

static int update_ref_path(struct send_ctx *sctx, struct recorded_ref *ref)
{
        int ret;
        struct fs_path *new_path;

        /*
         * Our reference's name member points to its full_path member string, so
         * we use here a new path.
         */
        new_path = fs_path_alloc();
        if (!new_path)
                return -ENOMEM;

        ret = get_cur_path(sctx, ref->dir, ref->dir_gen, new_path);
        if (ret < 0) {
                fs_path_free(new_path);
                return ret;
        }
        ret = fs_path_add(new_path, ref->name, ref->name_len);
        if (ret < 0) {
                fs_path_free(new_path);
                return ret;
        }

        fs_path_free(ref->full_path);
        set_ref_path(ref, new_path);

        return 0;
}

/*
 * When processing the new references for an inode we may orphanize an existing
 * directory inode because its old name conflicts with one of the new references
 * of the current inode. Later, when processing another new reference of our
 * inode, we might need to orphanize another inode, but the path we have in the
 * reference reflects the pre-orphanization name of the directory we previously
 * orphanized. For example:
 *
 * parent snapshot looks like:
 *
 * .                                     (ino 256)
 * |----- f1                             (ino 257)
 * |----- f2                             (ino 258)
 * |----- d1/                            (ino 259)
 *        |----- d2/                     (ino 260)
 *
 * send snapshot looks like:
 *
 * .                                     (ino 256)
 * |----- d1                             (ino 258)
 * |----- f2/                            (ino 259)
 *        |----- f2_link/                (ino 260)
 *        |       |----- f1              (ino 257)
 *        |
 *        |----- d2                      (ino 258)
 *
 * When processing inode 257 we compute the name for inode 259 as "d1", and we
 * cache it in the name cache. Later when we start processing inode 258, when
 * collecting all its new references we set a full path of "d1/d2" for its new
 * reference with name "d2". When we start processing the new references we
 * start by processing the new reference with name "d1", and this results in
 * orphanizing inode 259, since its old reference causes a conflict. Then we
 * move on the next new reference, with name "d2", and we find out we must
 * orphanize inode 260, as its old reference conflicts with ours - but for the
 * orphanization we use a source path corresponding to the path we stored in the
 * new reference, which is "d1/d2" and not "o259-6-0/d2" - this makes the
 * receiver fail since the path component "d1/" no longer exists, it was renamed
 * to "o259-6-0/" when processing the previous new reference. So in this case we
 * must recompute the path in the new reference and use it for the new
 * orphanization operation.
 */
static int refresh_ref_path(struct send_ctx *sctx, struct recorded_ref *ref)
{
        char AUTO_KFREE(name);
        int ret;

        name = kmemdup(ref->name, ref->name_len, GFP_KERNEL);
        if (!name)
                return -ENOMEM;

        fs_path_reset(ref->full_path);
        ret = get_cur_path(sctx, ref->dir, ref->dir_gen, ref->full_path);
        if (ret < 0)
                return ret;

        ret = fs_path_add(ref->full_path, name, ref->name_len);
        if (ret < 0)
                return ret;

        /* Update the reference's base name pointer. */
        set_ref_path(ref, ref->full_path);

        return 0;
}

static int rbtree_check_dir_ref_comp(const void *k, const struct rb_node *node)
{
        const struct recorded_ref *data = k;
        const struct recorded_ref *ref = rb_entry(node, struct recorded_ref, node);

        if (data->dir > ref->dir)
                return 1;
        if (data->dir < ref->dir)
                return -1;
        if (data->dir_gen > ref->dir_gen)
                return 1;
        if (data->dir_gen < ref->dir_gen)
                return -1;
        return 0;
}

static bool rbtree_check_dir_ref_less(struct rb_node *node, const struct rb_node *parent)
{
        const struct recorded_ref *entry = rb_entry(node, struct recorded_ref, node);

        return rbtree_check_dir_ref_comp(entry, parent) < 0;
}

static int record_check_dir_ref_in_tree(struct rb_root *root,
                        struct recorded_ref *ref, struct list_head *list)
{
        struct recorded_ref *tmp_ref;
        int ret;

        if (rb_find(ref, root, rbtree_check_dir_ref_comp))
                return 0;

        ret = dup_ref(ref, list);
        if (ret < 0)
                return ret;

        tmp_ref = list_last_entry(list, struct recorded_ref, list);
        rb_add(&tmp_ref->node, root, rbtree_check_dir_ref_less);
        tmp_ref->root = root;
        return 0;
}

static int rename_current_inode(struct send_ctx *sctx,
                                struct fs_path *current_path,
                                struct fs_path *new_path)
{
        int ret;

        ret = send_rename(sctx, current_path, new_path);
        if (ret < 0)
                return ret;

        ret = fs_path_copy(&sctx->cur_inode_path, new_path);
        if (ret < 0)
                return ret;

        return fs_path_copy(current_path, new_path);
}

/*
 * This does all the move/link/unlink/rmdir magic.
 */
static int process_recorded_refs(struct send_ctx *sctx, int *pending_move)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        int ret = 0;
        struct recorded_ref *cur;
        struct recorded_ref *cur2;
        LIST_HEAD(check_dirs);
        struct rb_root rbtree_check_dirs = RB_ROOT;
        struct fs_path *valid_path = NULL;
        u64 ow_inode = 0;
        u64 ow_gen;
        u64 ow_mode;
        bool did_overwrite = false;
        bool is_orphan = false;
        bool can_rename = true;
        bool orphanized_dir = false;
        bool orphanized_ancestor = false;

        /*
         * This should never happen as the root dir always has the same ref
         * which is always '..'
         */
        if (unlikely(sctx->cur_ino <= BTRFS_FIRST_FREE_OBJECTID)) {
                btrfs_err(fs_info,
                          "send: unexpected inode %llu in process_recorded_refs()",
                          sctx->cur_ino);
                ret = -EINVAL;
                goto out;
        }

        valid_path = fs_path_alloc();
        if (!valid_path) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * First, check if the first ref of the current inode was overwritten
         * before. If yes, we know that the current inode was already orphanized
         * and thus use the orphan name. If not, we can use get_cur_path to
         * get the path of the first ref as it would like while receiving at
         * this point in time.
         * New inodes are always orphan at the beginning, so force to use the
         * orphan name in this case.
         * The first ref is stored in valid_path and will be updated if it
         * gets moved around.
         */
        if (!sctx->cur_inode_new) {
                ret = did_overwrite_first_ref(sctx, sctx->cur_ino,
                                sctx->cur_inode_gen);
                if (ret < 0)
                        goto out;
                if (ret)
                        did_overwrite = true;
        }
        if (sctx->cur_inode_new || did_overwrite) {
                ret = gen_unique_name(sctx, sctx->cur_ino,
                                sctx->cur_inode_gen, valid_path);
                if (ret < 0)
                        goto out;
                is_orphan = true;
        } else {
                ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                valid_path);
                if (ret < 0)
                        goto out;
        }

        /*
         * Before doing any rename and link operations, do a first pass on the
         * new references to orphanize any unprocessed inodes that may have a
         * reference that conflicts with one of the new references of the current
         * inode. This needs to happen first because a new reference may conflict
         * with the old reference of a parent directory, so we must make sure
         * that the path used for link and rename commands don't use an
         * orphanized name when an ancestor was not yet orphanized.
         *
         * Example:
         *
         * Parent snapshot:
         *
         * .                                                      (ino 256)
         * |----- testdir/                                        (ino 259)
         * |          |----- a                                    (ino 257)
         * |
         * |----- b                                               (ino 258)
         *
         * Send snapshot:
         *
         * .                                                      (ino 256)
         * |----- testdir_2/                                      (ino 259)
         * |          |----- a                                    (ino 260)
         * |
         * |----- testdir                                         (ino 257)
         * |----- b                                               (ino 257)
         * |----- b2                                              (ino 258)
         *
         * Processing the new reference for inode 257 with name "b" may happen
         * before processing the new reference with name "testdir". If so, we
         * must make sure that by the time we send a link command to create the
         * hard link "b", inode 259 was already orphanized, since the generated
         * path in "valid_path" already contains the orphanized name for 259.
         * We are processing inode 257, so only later when processing 259 we do
         * the rename operation to change its temporary (orphanized) name to
         * "testdir_2".
         */
        list_for_each_entry(cur, &sctx->new_refs, list) {
                ret = get_cur_inode_state(sctx, cur->dir, cur->dir_gen, NULL, NULL);
                if (ret < 0)
                        goto out;
                if (ret == inode_state_will_create)
                        continue;

                /*
                 * Check if this new ref would overwrite the first ref of another
                 * unprocessed inode. If yes, orphanize the overwritten inode.
                 * If we find an overwritten ref that is not the first ref,
                 * simply unlink it.
                 */
                ret = will_overwrite_ref(sctx, cur->dir, cur->dir_gen,
                                cur->name, cur->name_len,
                                &ow_inode, &ow_gen, &ow_mode);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret = is_first_ref(sctx->parent_root,
                                           ow_inode, cur->dir, cur->name,
                                           cur->name_len);
                        if (ret < 0)
                                goto out;
                        if (ret) {
                                struct name_cache_entry *nce;
                                struct waiting_dir_move *wdm;

                                if (orphanized_dir) {
                                        ret = refresh_ref_path(sctx, cur);
                                        if (ret < 0)
                                                goto out;
                                }

                                ret = orphanize_inode(sctx, ow_inode, ow_gen,
                                                cur->full_path);
                                if (ret < 0)
                                        goto out;
                                if (S_ISDIR(ow_mode))
                                        orphanized_dir = true;

                                /*
                                 * If ow_inode has its rename operation delayed
                                 * make sure that its orphanized name is used in
                                 * the source path when performing its rename
                                 * operation.
                                 */
                                wdm = get_waiting_dir_move(sctx, ow_inode);
                                if (wdm)
                                        wdm->orphanized = true;

                                /*
                                 * Make sure we clear our orphanized inode's
                                 * name from the name cache. This is because the
                                 * inode ow_inode might be an ancestor of some
                                 * other inode that will be orphanized as well
                                 * later and has an inode number greater than
                                 * sctx->send_progress. We need to prevent
                                 * future name lookups from using the old name
                                 * and get instead the orphan name.
                                 */
                                nce = name_cache_search(sctx, ow_inode, ow_gen);
                                if (nce)
                                        btrfs_lru_cache_remove(&sctx->name_cache,
                                                               &nce->entry);

                                /*
                                 * ow_inode might currently be an ancestor of
                                 * cur_ino, therefore compute valid_path (the
                                 * current path of cur_ino) again because it
                                 * might contain the pre-orphanization name of
                                 * ow_inode, which is no longer valid.
                                 */
                                ret = is_ancestor(sctx->parent_root,
                                                  ow_inode, ow_gen,
                                                  sctx->cur_ino, NULL);
                                if (ret > 0) {
                                        orphanized_ancestor = true;
                                        fs_path_reset(valid_path);
                                        fs_path_reset(&sctx->cur_inode_path);
                                        ret = get_cur_path(sctx, sctx->cur_ino,
                                                           sctx->cur_inode_gen,
                                                           valid_path);
                                }
                                if (ret < 0)
                                        goto out;
                        } else {
                                /*
                                 * If we previously orphanized a directory that
                                 * collided with a new reference that we already
                                 * processed, recompute the current path because
                                 * that directory may be part of the path.
                                 */
                                if (orphanized_dir) {
                                        ret = refresh_ref_path(sctx, cur);
                                        if (ret < 0)
                                                goto out;
                                }
                                ret = send_unlink(sctx, cur->full_path);
                                if (ret < 0)
                                        goto out;
                        }
                }

        }

        list_for_each_entry(cur, &sctx->new_refs, list) {
                /*
                 * We may have refs where the parent directory does not exist
                 * yet. This happens if the parent directories inum is higher
                 * than the current inum. To handle this case, we create the
                 * parent directory out of order. But we need to check if this
                 * did already happen before due to other refs in the same dir.
                 */
                ret = get_cur_inode_state(sctx, cur->dir, cur->dir_gen, NULL, NULL);
                if (ret < 0)
                        goto out;
                if (ret == inode_state_will_create) {
                        ret = 0;
                        /*
                         * First check if any of the current inodes refs did
                         * already create the dir.
                         */
                        list_for_each_entry(cur2, &sctx->new_refs, list) {
                                if (cur == cur2)
                                        break;
                                if (cur2->dir == cur->dir) {
                                        ret = 1;
                                        break;
                                }
                        }

                        /*
                         * If that did not happen, check if a previous inode
                         * did already create the dir.
                         */
                        if (!ret)
                                ret = did_create_dir(sctx, cur->dir);
                        if (ret < 0)
                                goto out;
                        if (!ret) {
                                ret = send_create_inode(sctx, cur->dir);
                                if (ret < 0)
                                        goto out;
                                cache_dir_created(sctx, cur->dir);
                        }
                }

                if (S_ISDIR(sctx->cur_inode_mode) && sctx->parent_root) {
                        ret = wait_for_dest_dir_move(sctx, cur, is_orphan);
                        if (ret < 0)
                                goto out;
                        if (ret == 1) {
                                can_rename = false;
                                *pending_move = 1;
                        }
                }

                if (S_ISDIR(sctx->cur_inode_mode) && sctx->parent_root &&
                    can_rename) {
                        ret = wait_for_parent_move(sctx, cur, is_orphan);
                        if (ret < 0)
                                goto out;
                        if (ret == 1) {
                                can_rename = false;
                                *pending_move = 1;
                        }
                }

                /*
                 * link/move the ref to the new place. If we have an orphan
                 * inode, move it and update valid_path. If not, link or move
                 * it depending on the inode mode.
                 */
                if (is_orphan && can_rename) {
                        ret = rename_current_inode(sctx, valid_path, cur->full_path);
                        if (ret < 0)
                                goto out;
                        is_orphan = false;
                } else if (can_rename) {
                        if (S_ISDIR(sctx->cur_inode_mode)) {
                                /*
                                 * Dirs can't be linked, so move it. For moved
                                 * dirs, we always have one new and one deleted
                                 * ref. The deleted ref is ignored later.
                                 */
                                ret = rename_current_inode(sctx, valid_path,
                                                           cur->full_path);
                                if (ret < 0)
                                        goto out;
                        } else {
                                /*
                                 * We might have previously orphanized an inode
                                 * which is an ancestor of our current inode,
                                 * so our reference's full path, which was
                                 * computed before any such orphanizations, must
                                 * be updated.
                                 */
                                if (orphanized_dir) {
                                        ret = update_ref_path(sctx, cur);
                                        if (ret < 0)
                                                goto out;
                                }
                                ret = send_link(sctx, cur->full_path,
                                                valid_path);
                                if (ret < 0)
                                        goto out;
                        }
                }
                ret = record_check_dir_ref_in_tree(&rbtree_check_dirs, cur, &check_dirs);
                if (ret < 0)
                        goto out;
        }

        if (S_ISDIR(sctx->cur_inode_mode) && sctx->cur_inode_deleted) {
                /*
                 * Check if we can already rmdir the directory. If not,
                 * orphanize it. For every dir item inside that gets deleted
                 * later, we do this check again and rmdir it then if possible.
                 * See the use of check_dirs for more details.
                 */
                ret = can_rmdir(sctx, sctx->cur_ino, sctx->cur_inode_gen);
                if (ret < 0)
                        goto out;
                if (ret) {
                        ret = send_rmdir(sctx, valid_path);
                        if (ret < 0)
                                goto out;
                } else if (!is_orphan) {
                        ret = orphanize_inode(sctx, sctx->cur_ino,
                                        sctx->cur_inode_gen, valid_path);
                        if (ret < 0)
                                goto out;
                        is_orphan = true;
                }

                list_for_each_entry(cur, &sctx->deleted_refs, list) {
                        ret = record_check_dir_ref_in_tree(&rbtree_check_dirs, cur, &check_dirs);
                        if (ret < 0)
                                goto out;
                }
        } else if (S_ISDIR(sctx->cur_inode_mode) &&
                   !list_empty(&sctx->deleted_refs)) {
                /*
                 * We have a moved dir. Add the old parent to check_dirs
                 */
                cur = list_first_entry(&sctx->deleted_refs, struct recorded_ref, list);
                ret = record_check_dir_ref_in_tree(&rbtree_check_dirs, cur, &check_dirs);
                if (ret < 0)
                        goto out;
        } else if (!S_ISDIR(sctx->cur_inode_mode)) {
                /*
                 * We have a non dir inode. Go through all deleted refs and
                 * unlink them if they were not already overwritten by other
                 * inodes.
                 */
                list_for_each_entry(cur, &sctx->deleted_refs, list) {
                        ret = did_overwrite_ref(sctx, cur->dir, cur->dir_gen,
                                        sctx->cur_ino, sctx->cur_inode_gen,
                                        cur->name, cur->name_len);
                        if (ret < 0)
                                goto out;
                        if (!ret) {
                                /*
                                 * If we orphanized any ancestor before, we need
                                 * to recompute the full path for deleted names,
                                 * since any such path was computed before we
                                 * processed any references and orphanized any
                                 * ancestor inode.
                                 */
                                if (orphanized_ancestor) {
                                        ret = update_ref_path(sctx, cur);
                                        if (ret < 0)
                                                goto out;
                                }
                                ret = send_unlink(sctx, cur->full_path);
                                if (ret < 0)
                                        goto out;
                                if (is_current_inode_path(sctx, cur->full_path))
                                        fs_path_reset(&sctx->cur_inode_path);
                        }
                        ret = record_check_dir_ref_in_tree(&rbtree_check_dirs, cur, &check_dirs);
                        if (ret < 0)
                                goto out;
                }
                /*
                 * If the inode is still orphan, unlink the orphan. This may
                 * happen when a previous inode did overwrite the first ref
                 * of this inode and no new refs were added for the current
                 * inode. Unlinking does not mean that the inode is deleted in
                 * all cases. There may still be links to this inode in other
                 * places.
                 */
                if (is_orphan) {
                        ret = send_unlink(sctx, valid_path);
                        if (ret < 0)
                                goto out;
                }
        }

        /*
         * We did collect all parent dirs where cur_inode was once located. We
         * now go through all these dirs and check if they are pending for
         * deletion and if it's finally possible to perform the rmdir now.
         * We also update the inode stats of the parent dirs here.
         */
        list_for_each_entry(cur, &check_dirs, list) {
                /*
                 * In case we had refs into dirs that were not processed yet,
                 * we don't need to do the utime and rmdir logic for these dirs.
                 * The dir will be processed later.
                 */
                if (cur->dir > sctx->cur_ino)
                        continue;

                ret = get_cur_inode_state(sctx, cur->dir, cur->dir_gen, NULL, NULL);
                if (ret < 0)
                        goto out;

                if (ret == inode_state_did_create ||
                    ret == inode_state_no_change) {
                        ret = cache_dir_utimes(sctx, cur->dir, cur->dir_gen);
                        if (ret < 0)
                                goto out;
                } else if (ret == inode_state_did_delete) {
                        ret = can_rmdir(sctx, cur->dir, cur->dir_gen);
                        if (ret < 0)
                                goto out;
                        if (ret) {
                                ret = get_cur_path(sctx, cur->dir,
                                                   cur->dir_gen, valid_path);
                                if (ret < 0)
                                        goto out;
                                ret = send_rmdir(sctx, valid_path);
                                if (ret < 0)
                                        goto out;
                        }
                }
        }

        ret = 0;

out:
        __free_recorded_refs(&check_dirs);
        free_recorded_refs(sctx);
        fs_path_free(valid_path);
        return ret;
}

static int rbtree_ref_comp(const void *k, const struct rb_node *node)
{
        const struct recorded_ref *data = k;
        const struct recorded_ref *ref = rb_entry(node, struct recorded_ref, node);

        if (data->dir > ref->dir)
                return 1;
        if (data->dir < ref->dir)
                return -1;
        if (data->dir_gen > ref->dir_gen)
                return 1;
        if (data->dir_gen < ref->dir_gen)
                return -1;
        if (data->name_len > ref->name_len)
                return 1;
        if (data->name_len < ref->name_len)
                return -1;
        return strcmp(data->name, ref->name);
}

static bool rbtree_ref_less(struct rb_node *node, const struct rb_node *parent)
{
        const struct recorded_ref *entry = rb_entry(node, struct recorded_ref, node);

        return rbtree_ref_comp(entry, parent) < 0;
}

static int record_ref_in_tree(struct rb_root *root, struct list_head *refs,
                              struct fs_path *name, u64 dir, u64 dir_gen,
                              struct send_ctx *sctx)
{
        int ret = 0;
        struct fs_path *path = NULL;
        struct recorded_ref *ref = NULL;

        path = fs_path_alloc();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        ref = recorded_ref_alloc();
        if (!ref) {
                ret = -ENOMEM;
                goto out;
        }

        ret = get_cur_path(sctx, dir, dir_gen, path);
        if (ret < 0)
                goto out;
        ret = fs_path_add_path(path, name);
        if (ret < 0)
                goto out;

        ref->dir = dir;
        ref->dir_gen = dir_gen;
        set_ref_path(ref, path);
        list_add_tail(&ref->list, refs);
        rb_add(&ref->node, root, rbtree_ref_less);
        ref->root = root;
out:
        if (ret) {
                if (path && (!ref || !ref->full_path))
                        fs_path_free(path);
                recorded_ref_free(ref);
        }
        return ret;
}

static int record_new_ref_if_needed(u64 dir, struct fs_path *name, void *ctx)
{
        int ret;
        struct send_ctx *sctx = ctx;
        struct rb_node *node = NULL;
        struct recorded_ref data;
        struct recorded_ref *ref;
        u64 dir_gen;

        ret = get_inode_gen(sctx->send_root, dir, &dir_gen);
        if (ret < 0)
                return ret;

        data.dir = dir;
        data.dir_gen = dir_gen;
        set_ref_path(&data, name);
        node = rb_find(&data, &sctx->rbtree_deleted_refs, rbtree_ref_comp);
        if (node) {
                ref = rb_entry(node, struct recorded_ref, node);
                recorded_ref_free(ref);
        } else {
                ret = record_ref_in_tree(&sctx->rbtree_new_refs,
                                         &sctx->new_refs, name, dir, dir_gen,
                                         sctx);
        }

        return ret;
}

static int record_deleted_ref_if_needed(u64 dir, struct fs_path *name, void *ctx)
{
        int ret;
        struct send_ctx *sctx = ctx;
        struct rb_node *node = NULL;
        struct recorded_ref data;
        struct recorded_ref *ref;
        u64 dir_gen;

        ret = get_inode_gen(sctx->parent_root, dir, &dir_gen);
        if (ret < 0)
                return ret;

        data.dir = dir;
        data.dir_gen = dir_gen;
        set_ref_path(&data, name);
        node = rb_find(&data, &sctx->rbtree_new_refs, rbtree_ref_comp);
        if (node) {
                ref = rb_entry(node, struct recorded_ref, node);
                recorded_ref_free(ref);
        } else {
                ret = record_ref_in_tree(&sctx->rbtree_deleted_refs,
                                         &sctx->deleted_refs, name, dir,
                                         dir_gen, sctx);
        }

        return ret;
}

static int record_new_ref(struct send_ctx *sctx)
{
        int ret;

        ret = iterate_inode_ref(sctx->send_root, sctx->left_path, sctx->cmp_key,
                                false, record_new_ref_if_needed, sctx);
        if (ret < 0)
                return ret;

        return 0;
}

static int record_deleted_ref(struct send_ctx *sctx)
{
        int ret;

        ret = iterate_inode_ref(sctx->parent_root, sctx->right_path, sctx->cmp_key,
                                false, record_deleted_ref_if_needed, sctx);
        if (ret < 0)
                return ret;

        return 0;
}

static int record_changed_ref(struct send_ctx *sctx)
{
        int ret;

        ret = iterate_inode_ref(sctx->send_root, sctx->left_path, sctx->cmp_key,
                                false, record_new_ref_if_needed, sctx);
        if (ret < 0)
                return ret;
        ret = iterate_inode_ref(sctx->parent_root, sctx->right_path, sctx->cmp_key,
                                false, record_deleted_ref_if_needed, sctx);
        if (ret < 0)
                return ret;

        return 0;
}

/*
 * Record and process all refs at once. Needed when an inode changes the
 * generation number, which means that it was deleted and recreated.
 */
static int process_all_refs(struct send_ctx *sctx,
                            enum btrfs_compare_tree_result cmd)
{
        int ret = 0;
        int iter_ret = 0;
        struct btrfs_root *root;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct btrfs_key found_key;
        iterate_inode_ref_t cb;
        int pending_move = 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        if (cmd == BTRFS_COMPARE_TREE_NEW) {
                root = sctx->send_root;
                cb = record_new_ref_if_needed;
        } else if (cmd == BTRFS_COMPARE_TREE_DELETED) {
                root = sctx->parent_root;
                cb = record_deleted_ref_if_needed;
        } else {
                btrfs_err(sctx->send_root->fs_info,
                                "Wrong command %d in process_all_refs", cmd);
                return -EINVAL;
        }

        key.objectid = sctx->cmp_key->objectid;
        key.type = BTRFS_INODE_REF_KEY;
        key.offset = 0;
        btrfs_for_each_slot(root, &key, &found_key, path, iter_ret) {
                if (found_key.objectid != key.objectid ||
                    (found_key.type != BTRFS_INODE_REF_KEY &&
                     found_key.type != BTRFS_INODE_EXTREF_KEY))
                        break;

                ret = iterate_inode_ref(root, path, &found_key, false, cb, sctx);
                if (ret < 0)
                        return ret;
        }
        /* Catch error found during iteration */
        if (iter_ret < 0)
                return iter_ret;

        btrfs_release_path(path);

        /*
         * We don't actually care about pending_move as we are simply
         * re-creating this inode and will be rename'ing it into place once we
         * rename the parent directory.
         */
        return process_recorded_refs(sctx, &pending_move);
}

static int send_set_xattr(struct send_ctx *sctx,
                          const char *name, int name_len,
                          const char *data, int data_len)
{
        struct fs_path *path;
        int ret;

        path = get_cur_inode_path(sctx);
        if (IS_ERR(path))
                return PTR_ERR(path);

        ret = begin_cmd(sctx, BTRFS_SEND_C_SET_XATTR);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
        TLV_PUT_STRING(sctx, BTRFS_SEND_A_XATTR_NAME, name, name_len);
        TLV_PUT(sctx, BTRFS_SEND_A_XATTR_DATA, data, data_len);

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

static int send_remove_xattr(struct send_ctx *sctx,
                          struct fs_path *path,
                          const char *name, int name_len)
{
        int ret;

        ret = begin_cmd(sctx, BTRFS_SEND_C_REMOVE_XATTR);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
        TLV_PUT_STRING(sctx, BTRFS_SEND_A_XATTR_NAME, name, name_len);

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

static int __process_new_xattr(int num, struct btrfs_key *di_key,
                               const char *name, int name_len, const char *data,
                               int data_len, void *ctx)
{
        struct send_ctx *sctx = ctx;
        struct posix_acl_xattr_header dummy_acl;

        /* Capabilities are emitted by finish_inode_if_needed */
        if (!strncmp(name, XATTR_NAME_CAPS, name_len))
                return 0;

        /*
         * This hack is needed because empty acls are stored as zero byte
         * data in xattrs. Problem with that is, that receiving these zero byte
         * acls will fail later. To fix this, we send a dummy acl list that
         * only contains the version number and no entries.
         */
        if (!strncmp(name, XATTR_NAME_POSIX_ACL_ACCESS, name_len) ||
            !strncmp(name, XATTR_NAME_POSIX_ACL_DEFAULT, name_len)) {
                if (data_len == 0) {
                        dummy_acl.a_version =
                                        cpu_to_le32(POSIX_ACL_XATTR_VERSION);
                        data = (char *)&dummy_acl;
                        data_len = sizeof(dummy_acl);
                }
        }

        return send_set_xattr(sctx, name, name_len, data, data_len);
}

static int __process_deleted_xattr(int num, struct btrfs_key *di_key,
                                   const char *name, int name_len,
                                   const char *data, int data_len, void *ctx)
{
        struct send_ctx *sctx = ctx;
        struct fs_path *p;

        p = get_cur_inode_path(sctx);
        if (IS_ERR(p))
                return PTR_ERR(p);

        return send_remove_xattr(sctx, p, name, name_len);
}

static int process_new_xattr(struct send_ctx *sctx)
{
        return iterate_dir_item(sctx->send_root, sctx->left_path,
                                __process_new_xattr, sctx);
}

static int process_deleted_xattr(struct send_ctx *sctx)
{
        return iterate_dir_item(sctx->parent_root, sctx->right_path,
                                __process_deleted_xattr, sctx);
}

struct find_xattr_ctx {
        const char *name;
        int name_len;
        int found_idx;
        char *found_data;
        int found_data_len;
        bool copy_data;
};

static int __find_xattr(int num, struct btrfs_key *di_key, const char *name,
                        int name_len, const char *data, int data_len, void *vctx)
{
        struct find_xattr_ctx *ctx = vctx;

        if (name_len == ctx->name_len &&
            strncmp(name, ctx->name, name_len) == 0) {
                ctx->found_idx = num;
                ctx->found_data_len = data_len;
                if (ctx->copy_data) {
                        ctx->found_data = kmemdup(data, data_len, GFP_KERNEL);
                        if (!ctx->found_data)
                                return -ENOMEM;
                }
                return 1;
        }
        return 0;
}

static int find_xattr(struct btrfs_root *root,
                      struct btrfs_path *path,
                      struct btrfs_key *key,
                      const char *name, int name_len,
                      char **data, int *data_len)
{
        int ret;
        struct find_xattr_ctx ctx;

        ctx.name = name;
        ctx.name_len = name_len;
        ctx.found_idx = -1;
        ctx.found_data = NULL;
        ctx.found_data_len = 0;
        ctx.copy_data = (data != NULL);

        ret = iterate_dir_item(root, path, __find_xattr, &ctx);
        if (ret < 0)
                return ret;

        if (ctx.found_idx == -1)
                return -ENOENT;
        if (data) {
                *data = ctx.found_data;
                *data_len = ctx.found_data_len;
        } else {
                ASSERT(ctx.found_data == NULL);
        }
        return ctx.found_idx;
}


static int __process_changed_new_xattr(int num, struct btrfs_key *di_key,
                                       const char *name, int name_len,
                                       const char *data, int data_len,
                                       void *ctx)
{
        int ret;
        struct send_ctx *sctx = ctx;
        char AUTO_KFREE(found_data);
        int found_data_len = 0;

        ret = find_xattr(sctx->parent_root, sctx->right_path,
                         sctx->cmp_key, name, name_len, &found_data,
                         &found_data_len);
        if (ret == -ENOENT) {
                ret = __process_new_xattr(num, di_key, name, name_len, data,
                                          data_len, ctx);
        } else if (ret >= 0) {
                if (data_len != found_data_len ||
                    memcmp(data, found_data, data_len)) {
                        ret = __process_new_xattr(num, di_key, name, name_len,
                                                  data, data_len, ctx);
                } else {
                        ret = 0;
                }
        }

        return ret;
}

static int __process_changed_deleted_xattr(int num, struct btrfs_key *di_key,
                                           const char *name, int name_len,
                                           const char *data, int data_len,
                                           void *ctx)
{
        int ret;
        struct send_ctx *sctx = ctx;

        ret = find_xattr(sctx->send_root, sctx->left_path, sctx->cmp_key,
                         name, name_len, NULL, NULL);
        if (ret == -ENOENT)
                ret = __process_deleted_xattr(num, di_key, name, name_len, data,
                                              data_len, ctx);
        else if (ret >= 0)
                ret = 0;

        return ret;
}

static int process_changed_xattr(struct send_ctx *sctx)
{
        int ret;

        ret = iterate_dir_item(sctx->send_root, sctx->left_path,
                        __process_changed_new_xattr, sctx);
        if (ret < 0)
                return ret;

        return iterate_dir_item(sctx->parent_root, sctx->right_path,
                                __process_changed_deleted_xattr, sctx);
}

static int process_all_new_xattrs(struct send_ctx *sctx)
{
        int ret = 0;
        int iter_ret = 0;
        struct btrfs_root *root;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct btrfs_key found_key;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        root = sctx->send_root;

        key.objectid = sctx->cmp_key->objectid;
        key.type = BTRFS_XATTR_ITEM_KEY;
        key.offset = 0;
        btrfs_for_each_slot(root, &key, &found_key, path, iter_ret) {
                if (found_key.objectid != key.objectid ||
                    found_key.type != key.type) {
                        ret = 0;
                        break;
                }

                ret = iterate_dir_item(root, path, __process_new_xattr, sctx);
                if (ret < 0)
                        break;
        }
        /* Catch error found during iteration */
        if (iter_ret < 0)
                ret = iter_ret;

        return ret;
}

static int send_verity(struct send_ctx *sctx, struct fs_path *path,
                       struct fsverity_descriptor *desc)
{
        int ret;

        ret = begin_cmd(sctx, BTRFS_SEND_C_ENABLE_VERITY);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
        TLV_PUT_U8(sctx, BTRFS_SEND_A_VERITY_ALGORITHM,
                        le8_to_cpu(desc->hash_algorithm));
        TLV_PUT_U32(sctx, BTRFS_SEND_A_VERITY_BLOCK_SIZE,
                        1U << le8_to_cpu(desc->log_blocksize));
        TLV_PUT(sctx, BTRFS_SEND_A_VERITY_SALT_DATA, desc->salt,
                        le8_to_cpu(desc->salt_size));
        TLV_PUT(sctx, BTRFS_SEND_A_VERITY_SIG_DATA, desc->signature,
                        le32_to_cpu(desc->sig_size));

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

static int process_verity(struct send_ctx *sctx)
{
        int ret = 0;
        struct btrfs_inode *inode;
        struct fs_path *p;

        inode = btrfs_iget(sctx->cur_ino, sctx->send_root);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        ret = btrfs_get_verity_descriptor(&inode->vfs_inode, NULL, 0);
        if (ret < 0)
                goto iput;

        if (unlikely(ret > FS_VERITY_MAX_DESCRIPTOR_SIZE)) {
                ret = -EMSGSIZE;
                goto iput;
        }
        if (!sctx->verity_descriptor) {
                sctx->verity_descriptor = kvmalloc(FS_VERITY_MAX_DESCRIPTOR_SIZE,
                                                   GFP_KERNEL);
                if (!sctx->verity_descriptor) {
                        ret = -ENOMEM;
                        goto iput;
                }
        }

        ret = btrfs_get_verity_descriptor(&inode->vfs_inode, sctx->verity_descriptor, ret);
        if (ret < 0)
                goto iput;

        p = get_cur_inode_path(sctx);
        if (IS_ERR(p)) {
                ret = PTR_ERR(p);
                goto iput;
        }

        ret = send_verity(sctx, p, sctx->verity_descriptor);
iput:
        iput(&inode->vfs_inode);
        return ret;
}

static inline u64 max_send_read_size(const struct send_ctx *sctx)
{
        return sctx->send_max_size - SZ_16K;
}

static int put_data_header(struct send_ctx *sctx, u32 len)
{
        if (WARN_ON_ONCE(sctx->put_data))
                return -EINVAL;
        sctx->put_data = true;
        if (sctx->proto >= 2) {
                /*
                 * Since v2, the data attribute header doesn't include a length,
                 * it is implicitly to the end of the command.
                 */
                if (unlikely(sctx->send_max_size - sctx->send_size < sizeof(__le16) + len))
                        return -EOVERFLOW;
                put_unaligned_le16(BTRFS_SEND_A_DATA, sctx->send_buf + sctx->send_size);
                sctx->send_size += sizeof(__le16);
        } else {
                struct btrfs_tlv_header *hdr;

                if (unlikely(sctx->send_max_size - sctx->send_size < sizeof(*hdr) + len))
                        return -EOVERFLOW;
                hdr = (struct btrfs_tlv_header *)(sctx->send_buf + sctx->send_size);
                put_unaligned_le16(BTRFS_SEND_A_DATA, &hdr->tlv_type);
                put_unaligned_le16(len, &hdr->tlv_len);
                sctx->send_size += sizeof(*hdr);
        }
        return 0;
}

static int put_file_data(struct send_ctx *sctx, u64 offset, u32 len)
{
        struct btrfs_root *root = sctx->send_root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 cur = offset;
        const u64 end = offset + len;
        const pgoff_t last_index = ((end - 1) >> PAGE_SHIFT);
        struct address_space *mapping = sctx->cur_inode->i_mapping;
        int ret;

        ret = put_data_header(sctx, len);
        if (ret)
                return ret;

        while (cur < end) {
                pgoff_t index = (cur >> PAGE_SHIFT);
                unsigned int cur_len;
                unsigned int pg_offset;
                struct folio *folio;

                folio = filemap_lock_folio(mapping, index);
                if (IS_ERR(folio)) {
                        page_cache_sync_readahead(mapping,
                                                  &sctx->ra, NULL, index,
                                                  last_index + 1 - index);

                        folio = filemap_grab_folio(mapping, index);
                        if (IS_ERR(folio)) {
                                ret = PTR_ERR(folio);
                                break;
                        }
                }
                pg_offset = offset_in_folio(folio, cur);
                cur_len = min_t(unsigned int, end - cur, folio_size(folio) - pg_offset);

                if (folio_test_readahead(folio))
                        page_cache_async_readahead(mapping, &sctx->ra, NULL, folio,
                                                   last_index + 1 - index);

                if (!folio_test_uptodate(folio)) {
                        btrfs_read_folio(NULL, folio);
                        folio_lock(folio);
                        if (unlikely(!folio_test_uptodate(folio))) {
                                folio_unlock(folio);
                                btrfs_err(fs_info,
                        "send: IO error at offset %llu for inode %llu root %llu",
                                        folio_pos(folio), sctx->cur_ino,
                                        btrfs_root_id(sctx->send_root));
                                folio_put(folio);
                                ret = -EIO;
                                break;
                        }
                        if (folio->mapping != mapping) {
                                folio_unlock(folio);
                                folio_put(folio);
                                continue;
                        }
                }

                memcpy_from_folio(sctx->send_buf + sctx->send_size, folio,
                                  pg_offset, cur_len);
                folio_unlock(folio);
                folio_put(folio);
                cur += cur_len;
                sctx->send_size += cur_len;
        }

        return ret;
}

/*
 * Read some bytes from the current inode/file and send a write command to
 * user space.
 */
static int send_write(struct send_ctx *sctx, u64 offset, u32 len)
{
        int ret = 0;
        struct fs_path *p;

        p = get_cur_inode_path(sctx);
        if (IS_ERR(p))
                return PTR_ERR(p);

        ret = begin_cmd(sctx, BTRFS_SEND_C_WRITE);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        ret = put_file_data(sctx, offset, len);
        if (ret < 0)
                return ret;

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

/*
 * Send a clone command to user space.
 */
static int send_clone(struct send_ctx *sctx,
                      u64 offset, u32 len,
                      struct clone_root *clone_root)
{
        int ret = 0;
        struct fs_path *p;
        struct fs_path *cur_inode_path;
        u64 gen;

        cur_inode_path = get_cur_inode_path(sctx);
        if (IS_ERR(cur_inode_path))
                return PTR_ERR(cur_inode_path);

        p = fs_path_alloc();
        if (!p)
                return -ENOMEM;

        ret = begin_cmd(sctx, BTRFS_SEND_C_CLONE);
        if (ret < 0)
                goto out;

        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_LEN, len);
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, cur_inode_path);

        if (clone_root->root == sctx->send_root) {
                ret = get_inode_gen(sctx->send_root, clone_root->ino, &gen);
                if (ret < 0)
                        goto out;
                ret = get_cur_path(sctx, clone_root->ino, gen, p);
        } else {
                ret = get_inode_path(clone_root->root, clone_root->ino, p);
        }
        if (ret < 0)
                goto out;

        /*
         * If the parent we're using has a received_uuid set then use that as
         * our clone source as that is what we will look for when doing a
         * receive.
         *
         * This covers the case that we create a snapshot off of a received
         * subvolume and then use that as the parent and try to receive on a
         * different host.
         */
        if (!btrfs_is_empty_uuid(clone_root->root->root_item.received_uuid))
                TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                             clone_root->root->root_item.received_uuid);
        else
                TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                             clone_root->root->root_item.uuid);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_CTRANSID,
                    btrfs_root_ctransid(&clone_root->root->root_item));
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_CLONE_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_OFFSET,
                        clone_root->offset);

        ret = send_cmd(sctx);

tlv_put_failure:
out:
        fs_path_free(p);
        return ret;
}

/*
 * Send an update extent command to user space.
 */
static int send_update_extent(struct send_ctx *sctx,
                              u64 offset, u32 len)
{
        int ret = 0;
        struct fs_path *p;

        p = get_cur_inode_path(sctx);
        if (IS_ERR(p))
                return PTR_ERR(p);

        ret = begin_cmd(sctx, BTRFS_SEND_C_UPDATE_EXTENT);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_SIZE, len);

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

static int send_fallocate(struct send_ctx *sctx, u32 mode, u64 offset, u64 len)
{
        struct fs_path *path;
        int ret;

        path = get_cur_inode_path(sctx);
        if (IS_ERR(path))
                return PTR_ERR(path);

        ret = begin_cmd(sctx, BTRFS_SEND_C_FALLOCATE);
        if (ret < 0)
                return ret;

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
        TLV_PUT_U32(sctx, BTRFS_SEND_A_FALLOCATE_MODE, mode);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_SIZE, len);

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

static int send_hole(struct send_ctx *sctx, u64 end)
{
        struct fs_path *p = NULL;
        u64 read_size = max_send_read_size(sctx);
        u64 offset = sctx->cur_inode_last_extent;
        int ret = 0;

        /*
         * Starting with send stream v2 we have fallocate and can use it to
         * punch holes instead of sending writes full of zeroes.
         */
        if (proto_cmd_ok(sctx, BTRFS_SEND_C_FALLOCATE))
                return send_fallocate(sctx, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                                      offset, end - offset);

        /*
         * A hole that starts at EOF or beyond it. Since we do not yet support
         * fallocate (for extent preallocation and hole punching), sending a
         * write of zeroes starting at EOF or beyond would later require issuing
         * a truncate operation which would undo the write and achieve nothing.
         */
        if (offset >= sctx->cur_inode_size)
                return 0;

        /*
         * Don't go beyond the inode's i_size due to prealloc extents that start
         * after the i_size.
         */
        end = min_t(u64, end, sctx->cur_inode_size);

        if (sctx->flags & BTRFS_SEND_FLAG_NO_FILE_DATA)
                return send_update_extent(sctx, offset, end - offset);

        p = get_cur_inode_path(sctx);
        if (IS_ERR(p))
                return PTR_ERR(p);

        while (offset < end) {
                u64 len = min(end - offset, read_size);

                ret = begin_cmd(sctx, BTRFS_SEND_C_WRITE);
                if (ret < 0)
                        break;
                TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
                TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
                ret = put_data_header(sctx, len);
                if (ret < 0)
                        break;
                memset(sctx->send_buf + sctx->send_size, 0, len);
                sctx->send_size += len;
                ret = send_cmd(sctx);
                if (ret < 0)
                        break;
                offset += len;
        }
        sctx->cur_inode_next_write_offset = offset;
tlv_put_failure:
        return ret;
}

static int send_encoded_inline_extent(struct send_ctx *sctx,
                                      struct btrfs_path *path, u64 offset,
                                      u64 len)
{
        struct btrfs_fs_info *fs_info = sctx->send_root->fs_info;
        struct fs_path *fspath;
        struct extent_buffer *leaf = path->nodes[0];
        struct btrfs_key key;
        struct btrfs_file_extent_item *ei;
        u64 ram_bytes;
        size_t inline_size;
        int ret;

        fspath = get_cur_inode_path(sctx);
        if (IS_ERR(fspath))
                return PTR_ERR(fspath);

        ret = begin_cmd(sctx, BTRFS_SEND_C_ENCODED_WRITE);
        if (ret < 0)
                return ret;

        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
        ram_bytes = btrfs_file_extent_ram_bytes(leaf, ei);
        inline_size = btrfs_file_extent_inline_item_len(leaf, path->slots[0]);

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, fspath);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_UNENCODED_FILE_LEN,
                    min(key.offset + ram_bytes - offset, len));
        TLV_PUT_U64(sctx, BTRFS_SEND_A_UNENCODED_LEN, ram_bytes);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_UNENCODED_OFFSET, offset - key.offset);
        ret = btrfs_encoded_io_compression_from_extent(fs_info,
                                btrfs_file_extent_compression(leaf, ei));
        if (ret < 0)
                return ret;
        TLV_PUT_U32(sctx, BTRFS_SEND_A_COMPRESSION, ret);

        ret = put_data_header(sctx, inline_size);
        if (ret < 0)
                return ret;
        read_extent_buffer(leaf, sctx->send_buf + sctx->send_size,
                           btrfs_file_extent_inline_start(ei), inline_size);
        sctx->send_size += inline_size;

        ret = send_cmd(sctx);

tlv_put_failure:
        return ret;
}

static int send_encoded_extent(struct send_ctx *sctx, struct btrfs_path *path,
                               u64 offset, u64 len)
{
        struct btrfs_root *root = sctx->send_root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_inode *inode;
        struct fs_path *fspath;
        struct extent_buffer *leaf = path->nodes[0];
        struct btrfs_key key;
        struct btrfs_file_extent_item *ei;
        u64 disk_bytenr, disk_num_bytes;
        u32 data_offset;
        struct btrfs_cmd_header *hdr;
        u32 crc;
        int ret;

        inode = btrfs_iget(sctx->cur_ino, root);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        fspath = get_cur_inode_path(sctx);
        if (IS_ERR(fspath)) {
                ret = PTR_ERR(fspath);
                goto out;
        }

        ret = begin_cmd(sctx, BTRFS_SEND_C_ENCODED_WRITE);
        if (ret < 0)
                goto out;

        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
        disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
        disk_num_bytes = btrfs_file_extent_disk_num_bytes(leaf, ei);

        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, fspath);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_UNENCODED_FILE_LEN,
                    min(key.offset + btrfs_file_extent_num_bytes(leaf, ei) - offset,
                        len));
        TLV_PUT_U64(sctx, BTRFS_SEND_A_UNENCODED_LEN,
                    btrfs_file_extent_ram_bytes(leaf, ei));
        TLV_PUT_U64(sctx, BTRFS_SEND_A_UNENCODED_OFFSET,
                    offset - key.offset + btrfs_file_extent_offset(leaf, ei));
        ret = btrfs_encoded_io_compression_from_extent(fs_info,
                                btrfs_file_extent_compression(leaf, ei));
        if (ret < 0)
                goto out;
        TLV_PUT_U32(sctx, BTRFS_SEND_A_COMPRESSION, ret);
        TLV_PUT_U32(sctx, BTRFS_SEND_A_ENCRYPTION, 0);

        ret = put_data_header(sctx, disk_num_bytes);
        if (ret < 0)
                goto out;

        /*
         * We want to do I/O directly into the send buffer, so get the next page
         * boundary in the send buffer. This means that there may be a gap
         * between the beginning of the command and the file data.
         */
        data_offset = PAGE_ALIGN(sctx->send_size);
        if (unlikely(data_offset > sctx->send_max_size ||
                     sctx->send_max_size - data_offset < disk_num_bytes)) {
                ret = -EOVERFLOW;
                goto out;
        }

        /*
         * Note that send_buf is a mapping of send_buf_pages, so this is really
         * reading into send_buf.
         */
        ret = btrfs_encoded_read_regular_fill_pages(inode,
                                                    disk_bytenr, disk_num_bytes,
                                                    sctx->send_buf_pages +
                                                    (data_offset >> PAGE_SHIFT),
                                                    NULL);
        if (ret)
                goto out;

        hdr = (struct btrfs_cmd_header *)sctx->send_buf;
        hdr->len = cpu_to_le32(sctx->send_size + disk_num_bytes - sizeof(*hdr));
        hdr->crc = 0;
        crc = crc32c(0, sctx->send_buf, sctx->send_size);
        crc = crc32c(crc, sctx->send_buf + data_offset, disk_num_bytes);
        hdr->crc = cpu_to_le32(crc);

        ret = write_buf(sctx->send_filp, sctx->send_buf, sctx->send_size,
                        &sctx->send_off);
        if (!ret) {
                ret = write_buf(sctx->send_filp, sctx->send_buf + data_offset,
                                disk_num_bytes, &sctx->send_off);
        }
        sctx->send_size = 0;
        sctx->put_data = false;

tlv_put_failure:
out:
        iput(&inode->vfs_inode);
        return ret;
}

static int send_extent_data(struct send_ctx *sctx, struct btrfs_path *path,
                            const u64 offset, const u64 len)
{
        const u64 end = offset + len;
        struct extent_buffer *leaf = path->nodes[0];
        struct btrfs_file_extent_item *ei;
        u64 read_size = max_send_read_size(sctx);
        u64 sent = 0;

        if (sctx->flags & BTRFS_SEND_FLAG_NO_FILE_DATA)
                return send_update_extent(sctx, offset, len);

        ei = btrfs_item_ptr(leaf, path->slots[0],
                            struct btrfs_file_extent_item);
        if ((sctx->flags & BTRFS_SEND_FLAG_COMPRESSED) &&
            btrfs_file_extent_compression(leaf, ei) != BTRFS_COMPRESS_NONE) {
                bool is_inline = (btrfs_file_extent_type(leaf, ei) ==
                                  BTRFS_FILE_EXTENT_INLINE);

                /*
                 * Send the compressed extent unless the compressed data is
                 * larger than the decompressed data. This can happen if we're
                 * not sending the entire extent, either because it has been
                 * partially overwritten/truncated or because this is a part of
                 * the extent that we couldn't clone in clone_range().
                 */
                if (is_inline &&
                    btrfs_file_extent_inline_item_len(leaf,
                                                      path->slots[0]) <= len) {
                        return send_encoded_inline_extent(sctx, path, offset,
                                                          len);
                } else if (!is_inline &&
                           btrfs_file_extent_disk_num_bytes(leaf, ei) <= len) {
                        return send_encoded_extent(sctx, path, offset, len);
                }
        }

        if (sctx->cur_inode == NULL) {
                struct btrfs_inode *btrfs_inode;
                struct btrfs_root *root = sctx->send_root;

                btrfs_inode = btrfs_iget(sctx->cur_ino, root);
                if (IS_ERR(btrfs_inode))
                        return PTR_ERR(btrfs_inode);

                sctx->cur_inode = &btrfs_inode->vfs_inode;
                memset(&sctx->ra, 0, sizeof(struct file_ra_state));
                file_ra_state_init(&sctx->ra, sctx->cur_inode->i_mapping);

                /*
                 * It's very likely there are no pages from this inode in the page
                 * cache, so after reading extents and sending their data, we clean
                 * the page cache to avoid trashing the page cache (adding pressure
                 * to the page cache and forcing eviction of other data more useful
                 * for applications).
                 *
                 * We decide if we should clean the page cache simply by checking
                 * if the inode's mapping nrpages is 0 when we first open it, and
                 * not by using something like filemap_range_has_page() before
                 * reading an extent because when we ask the readahead code to
                 * read a given file range, it may (and almost always does) read
                 * pages from beyond that range (see the documentation for
                 * page_cache_sync_readahead()), so it would not be reliable,
                 * because after reading the first extent future calls to
                 * filemap_range_has_page() would return true because the readahead
                 * on the previous extent resulted in reading pages of the current
                 * extent as well.
                 */
                sctx->clean_page_cache = (sctx->cur_inode->i_mapping->nrpages == 0);
                sctx->page_cache_clear_start = round_down(offset, PAGE_SIZE);
        }

        while (sent < len) {
                u64 size = min(len - sent, read_size);
                int ret;

                ret = send_write(sctx, offset + sent, size);
                if (ret < 0)
                        return ret;
                sent += size;
        }

        if (sctx->clean_page_cache && PAGE_ALIGNED(end)) {
                /*
                 * Always operate only on ranges that are a multiple of the page
                 * size. This is not only to prevent zeroing parts of a page in
                 * the case of subpage sector size, but also to guarantee we evict
                 * pages, as passing a range that is smaller than page size does
                 * not evict the respective page (only zeroes part of its content).
                 *
                 * Always start from the end offset of the last range cleared.
                 * This is because the readahead code may (and very often does)
                 * reads pages beyond the range we request for readahead. So if
                 * we have an extent layout like this:
                 *
                 *            [ extent A ] [ extent B ] [ extent C ]
                 *
                 * When we ask page_cache_sync_readahead() to read extent A, it
                 * may also trigger reads for pages of extent B. If we are doing
                 * an incremental send and extent B has not changed between the
                 * parent and send snapshots, some or all of its pages may end
                 * up being read and placed in the page cache. So when truncating
                 * the page cache we always start from the end offset of the
                 * previously processed extent up to the end of the current
                 * extent.
                 */
                truncate_inode_pages_range(&sctx->cur_inode->i_data,
                                           sctx->page_cache_clear_start,
                                           end - 1);
                sctx->page_cache_clear_start = end;
        }

        return 0;
}

/*
 * Search for a capability xattr related to sctx->cur_ino. If the capability is
 * found, call send_set_xattr function to emit it.
 *
 * Return 0 if there isn't a capability, or when the capability was emitted
 * successfully, or < 0 if an error occurred.
 */
static int send_capabilities(struct send_ctx *sctx)
{
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_dir_item *di;
        struct extent_buffer *leaf;
        unsigned long data_ptr;
        char AUTO_KFREE(buf);
        int buf_len;
        int ret = 0;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        di = btrfs_lookup_xattr(NULL, sctx->send_root, path, sctx->cur_ino,
                                XATTR_NAME_CAPS, strlen(XATTR_NAME_CAPS), 0);
        if (!di) {
                /* There is no xattr for this inode */
                return 0;
        } else if (IS_ERR(di)) {
                return PTR_ERR(di);
        }

        leaf = path->nodes[0];
        buf_len = btrfs_dir_data_len(leaf, di);

        buf = kmalloc(buf_len, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        data_ptr = (unsigned long)(di + 1) + btrfs_dir_name_len(leaf, di);
        read_extent_buffer(leaf, buf, data_ptr, buf_len);

        ret = send_set_xattr(sctx, XATTR_NAME_CAPS,
                        strlen(XATTR_NAME_CAPS), buf, buf_len);
        return ret;
}

static int clone_range(struct send_ctx *sctx, struct btrfs_path *dst_path,
                       struct clone_root *clone_root, const u64 disk_byte,
                       u64 data_offset, u64 offset, u64 len)
{
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        int ret;
        struct btrfs_inode_info info;
        u64 clone_src_i_size = 0;

        /*
         * Prevent cloning from a zero offset with a length matching the sector
         * size because in some scenarios this will make the receiver fail.
         *
         * For example, if in the source filesystem the extent at offset 0
         * has a length of sectorsize and it was written using direct IO, then
         * it can never be an inline extent (even if compression is enabled).
         * Then this extent can be cloned in the original filesystem to a non
         * zero file offset, but it may not be possible to clone in the
         * destination filesystem because it can be inlined due to compression
         * on the destination filesystem (as the receiver's write operations are
         * always done using buffered IO). The same happens when the original
         * filesystem does not have compression enabled but the destination
         * filesystem has.
         */
        if (clone_root->offset == 0 &&
            len == sctx->send_root->fs_info->sectorsize)
                return send_extent_data(sctx, dst_path, offset, len);

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        /*
         * There are inodes that have extents that lie behind its i_size. Don't
         * accept clones from these extents.
         */
        ret = get_inode_info(clone_root->root, clone_root->ino, &info);
        btrfs_release_path(path);
        if (ret < 0)
                return ret;
        clone_src_i_size = info.size;

        /*
         * We can't send a clone operation for the entire range if we find
         * extent items in the respective range in the source file that
         * refer to different extents or if we find holes.
         * So check for that and do a mix of clone and regular write/copy
         * operations if needed.
         *
         * Example:
         *
         * mkfs.btrfs -f /dev/sda
         * mount /dev/sda /mnt
         * xfs_io -f -c "pwrite -S 0xaa 0K 100K" /mnt/foo
         * cp --reflink=always /mnt/foo /mnt/bar
         * xfs_io -c "pwrite -S 0xbb 50K 50K" /mnt/foo
         * btrfs subvolume snapshot -r /mnt /mnt/snap
         *
         * If when we send the snapshot and we are processing file bar (which
         * has a higher inode number than foo) we blindly send a clone operation
         * for the [0, 100K[ range from foo to bar, the receiver ends up getting
         * a file bar that matches the content of file foo - iow, doesn't match
         * the content from bar in the original filesystem.
         */
        key.objectid = clone_root->ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = clone_root->offset;
        ret = btrfs_search_slot(NULL, clone_root->root, &key, path, 0, 0);
        if (ret < 0)
                return ret;
        if (ret > 0 && path->slots[0] > 0) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0] - 1);
                if (key.objectid == clone_root->ino &&
                    key.type == BTRFS_EXTENT_DATA_KEY)
                        path->slots[0]--;
        }

        while (true) {
                struct extent_buffer *leaf = path->nodes[0];
                int slot = path->slots[0];
                struct btrfs_file_extent_item *ei;
                u8 type;
                u64 ext_len;
                u64 clone_len;
                u64 clone_data_offset;
                bool crossed_src_i_size = false;

                if (slot >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(clone_root->root, path);
                        if (ret < 0)
                                return ret;
                        else if (ret > 0)
                                break;
                        continue;
                }

                btrfs_item_key_to_cpu(leaf, &key, slot);

                /*
                 * We might have an implicit trailing hole (NO_HOLES feature
                 * enabled). We deal with it after leaving this loop.
                 */
                if (key.objectid != clone_root->ino ||
                    key.type != BTRFS_EXTENT_DATA_KEY)
                        break;

                ei = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
                type = btrfs_file_extent_type(leaf, ei);
                if (type == BTRFS_FILE_EXTENT_INLINE) {
                        ext_len = btrfs_file_extent_ram_bytes(leaf, ei);
                        ext_len = PAGE_ALIGN(ext_len);
                } else {
                        ext_len = btrfs_file_extent_num_bytes(leaf, ei);
                }

                if (key.offset + ext_len <= clone_root->offset)
                        goto next;

                if (key.offset > clone_root->offset) {
                        /* Implicit hole, NO_HOLES feature enabled. */
                        u64 hole_len = key.offset - clone_root->offset;

                        if (hole_len > len)
                                hole_len = len;
                        ret = send_extent_data(sctx, dst_path, offset,
                                               hole_len);
                        if (ret < 0)
                                return ret;

                        len -= hole_len;
                        if (len == 0)
                                break;
                        offset += hole_len;
                        clone_root->offset += hole_len;
                        data_offset += hole_len;
                }

                if (key.offset >= clone_root->offset + len)
                        break;

                if (key.offset >= clone_src_i_size)
                        break;

                if (key.offset + ext_len > clone_src_i_size) {
                        ext_len = clone_src_i_size - key.offset;
                        crossed_src_i_size = true;
                }

                clone_data_offset = btrfs_file_extent_offset(leaf, ei);
                if (btrfs_file_extent_disk_bytenr(leaf, ei) == disk_byte) {
                        clone_root->offset = key.offset;
                        if (clone_data_offset < data_offset &&
                                clone_data_offset + ext_len > data_offset) {
                                u64 extent_offset;

                                extent_offset = data_offset - clone_data_offset;
                                ext_len -= extent_offset;
                                clone_data_offset += extent_offset;
                                clone_root->offset += extent_offset;
                        }
                }

                clone_len = min_t(u64, ext_len, len);

                if (btrfs_file_extent_disk_bytenr(leaf, ei) == disk_byte &&
                    clone_data_offset == data_offset) {
                        const u64 src_end = clone_root->offset + clone_len;
                        const u64 sectorsize = SZ_64K;

                        /*
                         * We can't clone the last block, when its size is not
                         * sector size aligned, into the middle of a file. If we
                         * do so, the receiver will get a failure (-EINVAL) when
                         * trying to clone or will silently corrupt the data in
                         * the destination file if it's on a kernel without the
                         * fix introduced by commit ac765f83f1397646
                         * ("Btrfs: fix data corruption due to cloning of eof
                         * block).
                         *
                         * So issue a clone of the aligned down range plus a
                         * regular write for the eof block, if we hit that case.
                         *
                         * Also, we use the maximum possible sector size, 64K,
                         * because we don't know what's the sector size of the
                         * filesystem that receives the stream, so we have to
                         * assume the largest possible sector size.
                         */
                        if (src_end == clone_src_i_size &&
                            !IS_ALIGNED(src_end, sectorsize) &&
                            offset + clone_len < sctx->cur_inode_size) {
                                u64 slen;

                                slen = ALIGN_DOWN(src_end - clone_root->offset,
                                                  sectorsize);
                                if (slen > 0) {
                                        ret = send_clone(sctx, offset, slen,
                                                         clone_root);
                                        if (ret < 0)
                                                return ret;
                                }
                                ret = send_extent_data(sctx, dst_path,
                                                       offset + slen,
                                                       clone_len - slen);
                        } else {
                                ret = send_clone(sctx, offset, clone_len,
                                                 clone_root);
                        }
                } else if (crossed_src_i_size && clone_len < len) {
                        /*
                         * If we are at i_size of the clone source inode and we
                         * can not clone from it, terminate the loop. This is
                         * to avoid sending two write operations, one with a
                         * length matching clone_len and the final one after
                         * this loop with a length of len - clone_len.
                         *
                         * When using encoded writes (BTRFS_SEND_FLAG_COMPRESSED
                         * was passed to the send ioctl), this helps avoid
                         * sending an encoded write for an offset that is not
                         * sector size aligned, in case the i_size of the source
                         * inode is not sector size aligned. That will make the
                         * receiver fallback to decompression of the data and
                         * writing it using regular buffered IO, therefore while
                         * not incorrect, it's not optimal due decompression and
                         * possible re-compression at the receiver.
                         */
                        break;
                } else {
                        ret = send_extent_data(sctx, dst_path, offset,
                                               clone_len);
                }

                if (ret < 0)
                        return ret;

                len -= clone_len;
                if (len == 0)
                        break;
                offset += clone_len;
                clone_root->offset += clone_len;

                /*
                 * If we are cloning from the file we are currently processing,
                 * and using the send root as the clone root, we must stop once
                 * the current clone offset reaches the current eof of the file
                 * at the receiver, otherwise we would issue an invalid clone
                 * operation (source range going beyond eof) and cause the
                 * receiver to fail. So if we reach the current eof, bail out
                 * and fallback to a regular write.
                 */
                if (clone_root->root == sctx->send_root &&
                    clone_root->ino == sctx->cur_ino &&
                    clone_root->offset >= sctx->cur_inode_next_write_offset)
                        break;

                data_offset += clone_len;
next:
                path->slots[0]++;
        }

        if (len > 0)
                ret = send_extent_data(sctx, dst_path, offset, len);
        else
                ret = 0;
        return ret;
}

static int send_write_or_clone(struct send_ctx *sctx,
                               struct btrfs_path *path,
                               struct btrfs_key *key,
                               struct clone_root *clone_root)
{
        int ret = 0;
        u64 offset = key->offset;
        u64 end;
        u64 bs = sctx->send_root->fs_info->sectorsize;
        struct btrfs_file_extent_item *ei;
        u64 disk_byte;
        u64 data_offset;
        u64 num_bytes;
        struct btrfs_inode_info info = { 0 };

        end = min_t(u64, btrfs_file_extent_end(path), sctx->cur_inode_size);
        if (offset >= end)
                return 0;

        num_bytes = end - offset;

        if (!clone_root)
                goto write_data;

        if (IS_ALIGNED(end, bs))
                goto clone_data;

        /*
         * If the extent end is not aligned, we can clone if the extent ends at
         * the i_size of the inode and the clone range ends at the i_size of the
         * source inode, otherwise the clone operation fails with -EINVAL.
         */
        if (end != sctx->cur_inode_size)
                goto write_data;

        ret = get_inode_info(clone_root->root, clone_root->ino, &info);
        if (ret < 0)
                return ret;

        if (clone_root->offset + num_bytes == info.size) {
                /*
                 * The final size of our file matches the end offset, but it may
                 * be that its current size is larger, so we have to truncate it
                 * to any value between the start offset of the range and the
                 * final i_size, otherwise the clone operation is invalid
                 * because it's unaligned and it ends before the current EOF.
                 * We do this truncate to the final i_size when we finish
                 * processing the inode, but it's too late by then. And here we
                 * truncate to the start offset of the range because it's always
                 * sector size aligned while if it were the final i_size it
                 * would result in dirtying part of a page, filling part of a
                 * page with zeroes and then having the clone operation at the
                 * receiver trigger IO and wait for it due to the dirty page.
                 */
                if (sctx->parent_root != NULL) {
                        ret = send_truncate(sctx, sctx->cur_ino,
                                            sctx->cur_inode_gen, offset);
                        if (ret < 0)
                                return ret;
                }
                goto clone_data;
        }

write_data:
        ret = send_extent_data(sctx, path, offset, num_bytes);
        sctx->cur_inode_next_write_offset = end;
        return ret;

clone_data:
        ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                            struct btrfs_file_extent_item);
        disk_byte = btrfs_file_extent_disk_bytenr(path->nodes[0], ei);
        data_offset = btrfs_file_extent_offset(path->nodes[0], ei);
        ret = clone_range(sctx, path, clone_root, disk_byte, data_offset, offset,
                          num_bytes);
        sctx->cur_inode_next_write_offset = end;
        return ret;
}

static int is_extent_unchanged(struct send_ctx *sctx,
                               struct btrfs_path *left_path,
                               struct btrfs_key *ekey)
{
        int ret = 0;
        struct btrfs_key key;
        BTRFS_PATH_AUTO_FREE(path);
        struct extent_buffer *eb;
        int slot;
        struct btrfs_key found_key;
        struct btrfs_file_extent_item *ei;
        u64 left_disknr;
        u64 right_disknr;
        u64 left_offset;
        u64 right_offset;
        u64 left_offset_fixed;
        u64 left_len;
        u64 right_len;
        u64 left_gen;
        u64 right_gen;
        u8 left_type;
        u8 right_type;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        eb = left_path->nodes[0];
        slot = left_path->slots[0];
        ei = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
        left_type = btrfs_file_extent_type(eb, ei);

        if (left_type != BTRFS_FILE_EXTENT_REG)
                return 0;

        left_disknr = btrfs_file_extent_disk_bytenr(eb, ei);
        left_len = btrfs_file_extent_num_bytes(eb, ei);
        left_offset = btrfs_file_extent_offset(eb, ei);
        left_gen = btrfs_file_extent_generation(eb, ei);

        /*
         * Following comments will refer to these graphics. L is the left
         * extents which we are checking at the moment. 1-8 are the right
         * extents that we iterate.
         *
         *       |-----L-----|
         * |-1-|-2a-|-3-|-4-|-5-|-6-|
         *
         *       |-----L-----|
         * |--1--|-2b-|...(same as above)
         *
         * Alternative situation. Happens on files where extents got split.
         *       |-----L-----|
         * |-----------7-----------|-6-|
         *
         * Alternative situation. Happens on files which got larger.
         *       |-----L-----|
         * |-8-|
         * Nothing follows after 8.
         */

        key.objectid = ekey->objectid;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = ekey->offset;
        ret = btrfs_search_slot_for_read(sctx->parent_root, &key, path, 0, 0);
        if (ret < 0)
                return ret;
        if (ret)
                return 0;

        /*
         * Handle special case where the right side has no extents at all.
         */
        eb = path->nodes[0];
        slot = path->slots[0];
        btrfs_item_key_to_cpu(eb, &found_key, slot);
        if (found_key.objectid != key.objectid ||
            found_key.type != key.type)
                /* If we're a hole then just pretend nothing changed */
                return (left_disknr ? 0 : 1);

        /*
         * We're now on 2a, 2b or 7.
         */
        key = found_key;
        while (key.offset < ekey->offset + left_len) {
                ei = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
                right_type = btrfs_file_extent_type(eb, ei);
                if (right_type != BTRFS_FILE_EXTENT_REG &&
                    right_type != BTRFS_FILE_EXTENT_INLINE)
                        return 0;

                if (right_type == BTRFS_FILE_EXTENT_INLINE) {
                        right_len = btrfs_file_extent_ram_bytes(eb, ei);
                        right_len = PAGE_ALIGN(right_len);
                } else {
                        right_len = btrfs_file_extent_num_bytes(eb, ei);
                }

                /*
                 * Are we at extent 8? If yes, we know the extent is changed.
                 * This may only happen on the first iteration.
                 */
                if (found_key.offset + right_len <= ekey->offset)
                        /* If we're a hole just pretend nothing changed */
                        return (left_disknr ? 0 : 1);

                /*
                 * We just wanted to see if when we have an inline extent, what
                 * follows it is a regular extent (wanted to check the above
                 * condition for inline extents too). This should normally not
                 * happen but it's possible for example when we have an inline
                 * compressed extent representing data with a size matching
                 * the page size (currently the same as sector size).
                 */
                if (right_type == BTRFS_FILE_EXTENT_INLINE)
                        return 0;

                right_disknr = btrfs_file_extent_disk_bytenr(eb, ei);
                right_offset = btrfs_file_extent_offset(eb, ei);
                right_gen = btrfs_file_extent_generation(eb, ei);

                left_offset_fixed = left_offset;
                if (key.offset < ekey->offset) {
                        /* Fix the right offset for 2a and 7. */
                        right_offset += ekey->offset - key.offset;
                } else {
                        /* Fix the left offset for all behind 2a and 2b */
                        left_offset_fixed += key.offset - ekey->offset;
                }

                /*
                 * Check if we have the same extent.
                 */
                if (left_disknr != right_disknr ||
                    left_offset_fixed != right_offset ||
                    left_gen != right_gen)
                        return 0;

                /*
                 * Go to the next extent.
                 */
                ret = btrfs_next_item(sctx->parent_root, path);
                if (ret < 0)
                        return ret;
                if (!ret) {
                        eb = path->nodes[0];
                        slot = path->slots[0];
                        btrfs_item_key_to_cpu(eb, &found_key, slot);
                }
                if (ret || found_key.objectid != key.objectid ||
                    found_key.type != key.type) {
                        key.offset += right_len;
                        break;
                }
                if (found_key.offset != key.offset + right_len)
                        return 0;

                key = found_key;
        }

        /*
         * We're now behind the left extent (treat as unchanged) or at the end
         * of the right side (treat as changed).
         */
        if (key.offset >= ekey->offset + left_len)
                ret = 1;
        else
                ret = 0;

        return ret;
}

static int get_last_extent(struct send_ctx *sctx, u64 offset)
{
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_root *root = sctx->send_root;
        struct btrfs_key key;
        int ret;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        sctx->cur_inode_last_extent = 0;

        key.objectid = sctx->cur_ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = offset;
        ret = btrfs_search_slot_for_read(root, &key, path, 0, 1);
        if (ret < 0)
                return ret;
        ret = 0;
        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
        if (key.objectid != sctx->cur_ino || key.type != BTRFS_EXTENT_DATA_KEY)
                return ret;

        sctx->cur_inode_last_extent = btrfs_file_extent_end(path);
        return ret;
}

static int range_is_hole_in_parent(struct send_ctx *sctx,
                                   const u64 start,
                                   const u64 end)
{
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct btrfs_root *root = sctx->parent_root;
        u64 search_start = start;
        int ret;

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = sctx->cur_ino;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = search_start;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                return ret;
        if (ret > 0 && path->slots[0] > 0)
                path->slots[0]--;

        while (search_start < end) {
                struct extent_buffer *leaf = path->nodes[0];
                int slot = path->slots[0];
                struct btrfs_file_extent_item *fi;
                u64 extent_end;

                if (slot >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                return ret;
                        if (ret > 0)
                                break;
                        continue;
                }

                btrfs_item_key_to_cpu(leaf, &key, slot);
                if (key.objectid < sctx->cur_ino ||
                    key.type < BTRFS_EXTENT_DATA_KEY)
                        goto next;
                if (key.objectid > sctx->cur_ino ||
                    key.type > BTRFS_EXTENT_DATA_KEY ||
                    key.offset >= end)
                        break;

                fi = btrfs_item_ptr(leaf, slot, struct btrfs_file_extent_item);
                extent_end = btrfs_file_extent_end(path);
                if (extent_end <= start)
                        goto next;
                if (btrfs_file_extent_type(leaf, fi) == BTRFS_FILE_EXTENT_INLINE)
                        return 0;
                if (btrfs_file_extent_disk_bytenr(leaf, fi) == 0) {
                        search_start = extent_end;
                        goto next;
                }
                return 0;
next:
                path->slots[0]++;
        }
        return 1;
}

static int maybe_send_hole(struct send_ctx *sctx, struct btrfs_path *path,
                           struct btrfs_key *key)
{
        int ret = 0;

        if (sctx->cur_ino != key->objectid || !need_send_hole(sctx))
                return 0;

        /*
         * Get last extent's end offset (exclusive) if we haven't determined it
         * yet (we're processing the first file extent item that is new), or if
         * we're at the first slot of a leaf and the last extent's end is less
         * than the current extent's offset, because we might have skipped
         * entire leaves that contained only file extent items for our current
         * inode. These leaves have a generation number smaller (older) than the
         * one in the current leaf and the leaf our last extent came from, and
         * are located between these 2 leaves.
         */
        if ((sctx->cur_inode_last_extent == (u64)-1) ||
            (path->slots[0] == 0 && sctx->cur_inode_last_extent < key->offset)) {
                ret = get_last_extent(sctx, key->offset - 1);
                if (ret)
                        return ret;
        }

        if (sctx->cur_inode_last_extent < key->offset) {
                ret = range_is_hole_in_parent(sctx,
                                              sctx->cur_inode_last_extent,
                                              key->offset);
                if (ret < 0)
                        return ret;
                else if (ret == 0)
                        ret = send_hole(sctx, key->offset);
                else
                        ret = 0;
        }
        sctx->cur_inode_last_extent = btrfs_file_extent_end(path);
        return ret;
}

static int process_extent(struct send_ctx *sctx,
                          struct btrfs_path *path,
                          struct btrfs_key *key)
{
        struct clone_root *found_clone = NULL;
        int ret = 0;

        if (S_ISLNK(sctx->cur_inode_mode))
                return 0;

        if (sctx->parent_root && !sctx->cur_inode_new) {
                ret = is_extent_unchanged(sctx, path, key);
                if (ret < 0)
                        return ret;
                if (ret)
                        goto out_hole;
        } else {
                struct btrfs_file_extent_item *ei;
                u8 type;

                ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                    struct btrfs_file_extent_item);
                type = btrfs_file_extent_type(path->nodes[0], ei);
                if (type == BTRFS_FILE_EXTENT_PREALLOC ||
                    type == BTRFS_FILE_EXTENT_REG) {
                        /*
                         * The send spec does not have a prealloc command yet,
                         * so just leave a hole for prealloc'ed extents until
                         * we have enough commands queued up to justify rev'ing
                         * the send spec.
                         */
                        if (type == BTRFS_FILE_EXTENT_PREALLOC)
                                return 0;

                        /* Have a hole, just skip it. */
                        if (btrfs_file_extent_disk_bytenr(path->nodes[0], ei) == 0)
                                return 0;
                }
        }

        ret = find_extent_clone(sctx, path, key->objectid, key->offset,
                        sctx->cur_inode_size, &found_clone);
        if (ret != -ENOENT && ret < 0)
                return ret;

        ret = send_write_or_clone(sctx, path, key, found_clone);
        if (ret)
                return ret;
out_hole:
        return maybe_send_hole(sctx, path, key);
}

static int process_all_extents(struct send_ctx *sctx)
{
        int ret = 0;
        int iter_ret = 0;
        struct btrfs_root *root;
        BTRFS_PATH_AUTO_FREE(path);
        struct btrfs_key key;
        struct btrfs_key found_key;

        root = sctx->send_root;
        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;

        key.objectid = sctx->cmp_key->objectid;
        key.type = BTRFS_EXTENT_DATA_KEY;
        key.offset = 0;
        btrfs_for_each_slot(root, &key, &found_key, path, iter_ret) {
                if (found_key.objectid != key.objectid ||
                    found_key.type != key.type) {
                        ret = 0;
                        break;
                }

                ret = process_extent(sctx, path, &found_key);
                if (ret < 0)
                        break;
        }
        /* Catch error found during iteration */
        if (iter_ret < 0)
                ret = iter_ret;

        return ret;
}

static int process_recorded_refs_if_needed(struct send_ctx *sctx, bool at_end,
                                           int *pending_move,
                                           int *refs_processed)
{
        int ret;

        if (sctx->cur_ino == 0)
                return 0;

        if (!at_end && sctx->cur_ino == sctx->cmp_key->objectid &&
            sctx->cmp_key->type <= BTRFS_INODE_EXTREF_KEY)
                return 0;

        if (list_empty(&sctx->new_refs) && list_empty(&sctx->deleted_refs))
                return 0;

        ret = process_recorded_refs(sctx, pending_move);
        if (ret < 0)
                return ret;

        *refs_processed = 1;
        return 0;
}

static int finish_inode_if_needed(struct send_ctx *sctx, bool at_end)
{
        int ret = 0;
        struct btrfs_inode_info info;
        u64 left_mode;
        u64 left_uid;
        u64 left_gid;
        u64 left_fileattr;
        u64 right_mode;
        u64 right_uid;
        u64 right_gid;
        u64 right_fileattr;
        int need_chmod = 0;
        int need_chown = 0;
        bool need_fileattr = false;
        int need_truncate = 1;
        int pending_move = 0;
        int refs_processed = 0;

        if (sctx->ignore_cur_inode)
                return 0;

        ret = process_recorded_refs_if_needed(sctx, at_end, &pending_move,
                                              &refs_processed);
        if (ret < 0)
                goto out;

        /*
         * We have processed the refs and thus need to advance send_progress.
         * Now, calls to get_cur_xxx will take the updated refs of the current
         * inode into account.
         *
         * On the other hand, if our current inode is a directory and couldn't
         * be moved/renamed because its parent was renamed/moved too and it has
         * a higher inode number, we can only move/rename our current inode
         * after we moved/renamed its parent. Therefore in this case operate on
         * the old path (pre move/rename) of our current inode, and the
         * move/rename will be performed later.
         */
        if (refs_processed && !pending_move)
                sctx->send_progress = sctx->cur_ino + 1;

        if (sctx->cur_ino == 0 || sctx->cur_inode_deleted)
                goto out;
        if (!at_end && sctx->cmp_key->objectid == sctx->cur_ino)
                goto out;
        ret = get_inode_info(sctx->send_root, sctx->cur_ino, &info);
        if (ret < 0)
                goto out;
        left_mode = info.mode;
        left_uid = info.uid;
        left_gid = info.gid;
        left_fileattr = info.fileattr;

        if (!sctx->parent_root || sctx->cur_inode_new) {
                need_chown = 1;
                if (!S_ISLNK(sctx->cur_inode_mode))
                        need_chmod = 1;
                if (sctx->cur_inode_next_write_offset == sctx->cur_inode_size)
                        need_truncate = 0;
        } else {
                u64 old_size;

                ret = get_inode_info(sctx->parent_root, sctx->cur_ino, &info);
                if (ret < 0)
                        goto out;
                old_size = info.size;
                right_mode = info.mode;
                right_uid = info.uid;
                right_gid = info.gid;
                right_fileattr = info.fileattr;

                if (left_uid != right_uid || left_gid != right_gid)
                        need_chown = 1;
                if (!S_ISLNK(sctx->cur_inode_mode) && left_mode != right_mode)
                        need_chmod = 1;
                if (!S_ISLNK(sctx->cur_inode_mode) && left_fileattr != right_fileattr)
                        need_fileattr = true;
                if ((old_size == sctx->cur_inode_size) ||
                    (sctx->cur_inode_size > old_size &&
                     sctx->cur_inode_next_write_offset == sctx->cur_inode_size))
                        need_truncate = 0;
        }

        if (S_ISREG(sctx->cur_inode_mode)) {
                if (need_send_hole(sctx)) {
                        if (sctx->cur_inode_last_extent == (u64)-1 ||
                            sctx->cur_inode_last_extent <
                            sctx->cur_inode_size) {
                                ret = get_last_extent(sctx, (u64)-1);
                                if (ret)
                                        goto out;
                        }
                        if (sctx->cur_inode_last_extent < sctx->cur_inode_size) {
                                ret = range_is_hole_in_parent(sctx,
                                                      sctx->cur_inode_last_extent,
                                                      sctx->cur_inode_size);
                                if (ret < 0) {
                                        goto out;
                                } else if (ret == 0) {
                                        ret = send_hole(sctx, sctx->cur_inode_size);
                                        if (ret < 0)
                                                goto out;
                                } else {
                                        /* Range is already a hole, skip. */
                                        ret = 0;
                                }
                        }
                }
                if (need_truncate) {
                        ret = send_truncate(sctx, sctx->cur_ino,
                                            sctx->cur_inode_gen,
                                            sctx->cur_inode_size);
                        if (ret < 0)
                                goto out;
                }
        }

        if (need_chown) {
                ret = send_chown(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                left_uid, left_gid);
                if (ret < 0)
                        goto out;
        }
        if (need_chmod) {
                ret = send_chmod(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                left_mode);
                if (ret < 0)
                        goto out;
        }
        if (need_fileattr) {
                ret = send_fileattr(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                                    left_fileattr);
                if (ret < 0)
                        goto out;
        }

        if (proto_cmd_ok(sctx, BTRFS_SEND_C_ENABLE_VERITY)
            && sctx->cur_inode_needs_verity) {
                ret = process_verity(sctx);
                if (ret < 0)
                        goto out;
        }

        ret = send_capabilities(sctx);
        if (ret < 0)
                goto out;

        /*
         * If other directory inodes depended on our current directory
         * inode's move/rename, now do their move/rename operations.
         */
        if (!is_waiting_for_move(sctx, sctx->cur_ino)) {
                ret = apply_children_dir_moves(sctx);
                if (ret)
                        goto out;
                /*
                 * Need to send that every time, no matter if it actually
                 * changed between the two trees as we have done changes to
                 * the inode before. If our inode is a directory and it's
                 * waiting to be moved/renamed, we will send its utimes when
                 * it's moved/renamed, therefore we don't need to do it here.
                 */
                sctx->send_progress = sctx->cur_ino + 1;

                /*
                 * If the current inode is a non-empty directory, delay issuing
                 * the utimes command for it, as it's very likely we have inodes
                 * with an higher number inside it. We want to issue the utimes
                 * command only after adding all dentries to it.
                 */
                if (S_ISDIR(sctx->cur_inode_mode) && sctx->cur_inode_size > 0)
                        ret = cache_dir_utimes(sctx, sctx->cur_ino, sctx->cur_inode_gen);
                else
                        ret = send_utimes(sctx, sctx->cur_ino, sctx->cur_inode_gen);

                if (ret < 0)
                        goto out;
        }

out:
        if (!ret)
                ret = trim_dir_utimes_cache(sctx);

        return ret;
}

static void close_current_inode(struct send_ctx *sctx)
{
        u64 i_size;

        if (sctx->cur_inode == NULL)
                return;

        i_size = i_size_read(sctx->cur_inode);

        /*
         * If we are doing an incremental send, we may have extents between the
         * last processed extent and the i_size that have not been processed
         * because they haven't changed but we may have read some of their pages
         * through readahead, see the comments at send_extent_data().
         */
        if (sctx->clean_page_cache && sctx->page_cache_clear_start < i_size)
                truncate_inode_pages_range(&sctx->cur_inode->i_data,
                                           sctx->page_cache_clear_start,
                                           round_up(i_size, PAGE_SIZE) - 1);

        iput(sctx->cur_inode);
        sctx->cur_inode = NULL;
}

static int changed_inode(struct send_ctx *sctx,
                         enum btrfs_compare_tree_result result)
{
        int ret;
        struct btrfs_key *key = sctx->cmp_key;
        struct btrfs_inode_item *left_ii = NULL;
        struct btrfs_inode_item *right_ii = NULL;
        u64 left_gen = 0;
        u64 right_gen = 0;

        close_current_inode(sctx);

        sctx->cur_ino = key->objectid;
        sctx->cur_inode_new_gen = false;
        sctx->cur_inode_last_extent = (u64)-1;
        sctx->cur_inode_next_write_offset = 0;
        sctx->ignore_cur_inode = false;
        fs_path_reset(&sctx->cur_inode_path);

        /*
         * Set send_progress to current inode. This will tell all get_cur_xxx
         * functions that the current inode's refs are not updated yet. Later,
         * when process_recorded_refs is finished, it is set to cur_ino + 1.
         */
        sctx->send_progress = sctx->cur_ino;

        if (result == BTRFS_COMPARE_TREE_NEW ||
            result == BTRFS_COMPARE_TREE_CHANGED) {
                left_ii = btrfs_item_ptr(sctx->left_path->nodes[0],
                                sctx->left_path->slots[0],
                                struct btrfs_inode_item);
                left_gen = btrfs_inode_generation(sctx->left_path->nodes[0],
                                left_ii);
        } else {
                right_ii = btrfs_item_ptr(sctx->right_path->nodes[0],
                                sctx->right_path->slots[0],
                                struct btrfs_inode_item);
                right_gen = btrfs_inode_generation(sctx->right_path->nodes[0],
                                right_ii);
        }
        if (result == BTRFS_COMPARE_TREE_CHANGED) {
                right_ii = btrfs_item_ptr(sctx->right_path->nodes[0],
                                sctx->right_path->slots[0],
                                struct btrfs_inode_item);

                right_gen = btrfs_inode_generation(sctx->right_path->nodes[0],
                                right_ii);

                /*
                 * The cur_ino = root dir case is special here. We can't treat
                 * the inode as deleted+reused because it would generate a
                 * stream that tries to delete/mkdir the root dir.
                 */
                if (left_gen != right_gen &&
                    sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID)
                        sctx->cur_inode_new_gen = true;
        }

        /*
         * Normally we do not find inodes with a link count of zero (orphans)
         * because the most common case is to create a snapshot and use it
         * for a send operation. However other less common use cases involve
         * using a subvolume and send it after turning it to RO mode just
         * after deleting all hard links of a file while holding an open
         * file descriptor against it or turning a RO snapshot into RW mode,
         * keep an open file descriptor against a file, delete it and then
         * turn the snapshot back to RO mode before using it for a send
         * operation. The former is what the receiver operation does.
         * Therefore, if we want to send these snapshots soon after they're
         * received, we need to handle orphan inodes as well. Moreover, orphans
         * can appear not only in the send snapshot but also in the parent
         * snapshot. Here are several cases:
         *
         * Case 1: BTRFS_COMPARE_TREE_NEW
         *       |  send snapshot  | action
         * --------------------------------
         * nlink |        0        | ignore
         *
         * Case 2: BTRFS_COMPARE_TREE_DELETED
         *       | parent snapshot | action
         * ----------------------------------
         * nlink |        0        | as usual
         * Note: No unlinks will be sent because there're no paths for it.
         *
         * Case 3: BTRFS_COMPARE_TREE_CHANGED
         *           |       | parent snapshot | send snapshot | action
         * -----------------------------------------------------------------------
         * subcase 1 | nlink |        0        |       0       | ignore
         * subcase 2 | nlink |       >0        |       0       | new_gen(deletion)
         * subcase 3 | nlink |        0        |      >0       | new_gen(creation)
         *
         */
        if (result == BTRFS_COMPARE_TREE_NEW) {
                if (btrfs_inode_nlink(sctx->left_path->nodes[0], left_ii) == 0) {
                        sctx->ignore_cur_inode = true;
                        return 0;
                }
                sctx->cur_inode_gen = left_gen;
                sctx->cur_inode_new = true;
                sctx->cur_inode_deleted = false;
                sctx->cur_inode_size = btrfs_inode_size(
                                sctx->left_path->nodes[0], left_ii);
                sctx->cur_inode_mode = btrfs_inode_mode(
                                sctx->left_path->nodes[0], left_ii);
                sctx->cur_inode_rdev = btrfs_inode_rdev(
                                sctx->left_path->nodes[0], left_ii);
                if (sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID)
                        ret = send_create_inode_if_needed(sctx);
        } else if (result == BTRFS_COMPARE_TREE_DELETED) {
                sctx->cur_inode_gen = right_gen;
                sctx->cur_inode_new = false;
                sctx->cur_inode_deleted = true;
                sctx->cur_inode_size = btrfs_inode_size(
                                sctx->right_path->nodes[0], right_ii);
                sctx->cur_inode_mode = btrfs_inode_mode(
                                sctx->right_path->nodes[0], right_ii);
        } else if (result == BTRFS_COMPARE_TREE_CHANGED) {
                u32 new_nlinks, old_nlinks;

                new_nlinks = btrfs_inode_nlink(sctx->left_path->nodes[0], left_ii);
                old_nlinks = btrfs_inode_nlink(sctx->right_path->nodes[0], right_ii);
                if (new_nlinks == 0 && old_nlinks == 0) {
                        sctx->ignore_cur_inode = true;
                        return 0;
                } else if (new_nlinks == 0 || old_nlinks == 0) {
                        sctx->cur_inode_new_gen = 1;
                }
                /*
                 * We need to do some special handling in case the inode was
                 * reported as changed with a changed generation number. This
                 * means that the original inode was deleted and new inode
                 * reused the same inum. So we have to treat the old inode as
                 * deleted and the new one as new.
                 */
                if (sctx->cur_inode_new_gen) {
                        /*
                         * First, process the inode as if it was deleted.
                         */
                        if (old_nlinks > 0) {
                                sctx->cur_inode_gen = right_gen;
                                sctx->cur_inode_new = false;
                                sctx->cur_inode_deleted = true;
                                sctx->cur_inode_size = btrfs_inode_size(
                                                sctx->right_path->nodes[0], right_ii);
                                sctx->cur_inode_mode = btrfs_inode_mode(
                                                sctx->right_path->nodes[0], right_ii);
                                ret = process_all_refs(sctx,
                                                BTRFS_COMPARE_TREE_DELETED);
                                if (ret < 0)
                                        return ret;
                        }

                        /*
                         * Now process the inode as if it was new.
                         */
                        if (new_nlinks > 0) {
                                sctx->cur_inode_gen = left_gen;
                                sctx->cur_inode_new = true;
                                sctx->cur_inode_deleted = false;
                                sctx->cur_inode_size = btrfs_inode_size(
                                                sctx->left_path->nodes[0],
                                                left_ii);
                                sctx->cur_inode_mode = btrfs_inode_mode(
                                                sctx->left_path->nodes[0],
                                                left_ii);
                                sctx->cur_inode_rdev = btrfs_inode_rdev(
                                                sctx->left_path->nodes[0],
                                                left_ii);
                                ret = send_create_inode_if_needed(sctx);
                                if (ret < 0)
                                        return ret;

                                ret = process_all_refs(sctx, BTRFS_COMPARE_TREE_NEW);
                                if (ret < 0)
                                        return ret;
                                /*
                                 * Advance send_progress now as we did not get
                                 * into process_recorded_refs_if_needed in the
                                 * new_gen case.
                                 */
                                sctx->send_progress = sctx->cur_ino + 1;

                                /*
                                 * Now process all extents and xattrs of the
                                 * inode as if they were all new.
                                 */
                                ret = process_all_extents(sctx);
                                if (ret < 0)
                                        return ret;
                                ret = process_all_new_xattrs(sctx);
                                if (ret < 0)
                                        return ret;
                        }
                } else {
                        sctx->cur_inode_gen = left_gen;
                        sctx->cur_inode_new = false;
                        sctx->cur_inode_new_gen = false;
                        sctx->cur_inode_deleted = false;
                        sctx->cur_inode_size = btrfs_inode_size(
                                        sctx->left_path->nodes[0], left_ii);
                        sctx->cur_inode_mode = btrfs_inode_mode(
                                        sctx->left_path->nodes[0], left_ii);
                }
        }

        return 0;
}

/*
 * We have to process new refs before deleted refs, but compare_trees gives us
 * the new and deleted refs mixed. To fix this, we record the new/deleted refs
 * first and later process them in process_recorded_refs.
 * For the cur_inode_new_gen case, we skip recording completely because
 * changed_inode did already initiate processing of refs. The reason for this is
 * that in this case, compare_tree actually compares the refs of 2 different
 * inodes. To fix this, process_all_refs is used in changed_inode to handle all
 * refs of the right tree as deleted and all refs of the left tree as new.
 */
static int changed_ref(struct send_ctx *sctx,
                       enum btrfs_compare_tree_result result)
{
        int ret = 0;

        if (unlikely(sctx->cur_ino != sctx->cmp_key->objectid)) {
                inconsistent_snapshot_error(sctx, result, "reference");
                return -EIO;
        }

        if (!sctx->cur_inode_new_gen &&
            sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID) {
                if (result == BTRFS_COMPARE_TREE_NEW)
                        ret = record_new_ref(sctx);
                else if (result == BTRFS_COMPARE_TREE_DELETED)
                        ret = record_deleted_ref(sctx);
                else if (result == BTRFS_COMPARE_TREE_CHANGED)
                        ret = record_changed_ref(sctx);
        }

        return ret;
}

/*
 * Process new/deleted/changed xattrs. We skip processing in the
 * cur_inode_new_gen case because changed_inode did already initiate processing
 * of xattrs. The reason is the same as in changed_ref
 */
static int changed_xattr(struct send_ctx *sctx,
                         enum btrfs_compare_tree_result result)
{
        int ret = 0;

        if (unlikely(sctx->cur_ino != sctx->cmp_key->objectid)) {
                inconsistent_snapshot_error(sctx, result, "xattr");
                return -EIO;
        }

        if (!sctx->cur_inode_new_gen && !sctx->cur_inode_deleted) {
                if (result == BTRFS_COMPARE_TREE_NEW)
                        ret = process_new_xattr(sctx);
                else if (result == BTRFS_COMPARE_TREE_DELETED)
                        ret = process_deleted_xattr(sctx);
                else if (result == BTRFS_COMPARE_TREE_CHANGED)
                        ret = process_changed_xattr(sctx);
        }

        return ret;
}

/*
 * Process new/deleted/changed extents. We skip processing in the
 * cur_inode_new_gen case because changed_inode did already initiate processing
 * of extents. The reason is the same as in changed_ref
 */
static int changed_extent(struct send_ctx *sctx,
                          enum btrfs_compare_tree_result result)
{
        int ret = 0;

        /*
         * We have found an extent item that changed without the inode item
         * having changed. This can happen either after relocation (where the
         * disk_bytenr of an extent item is replaced at
         * relocation.c:replace_file_extents()) or after deduplication into a
         * file in both the parent and send snapshots (where an extent item can
         * get modified or replaced with a new one). Note that deduplication
         * updates the inode item, but it only changes the iversion (sequence
         * field in the inode item) of the inode, so if a file is deduplicated
         * the same amount of times in both the parent and send snapshots, its
         * iversion becomes the same in both snapshots, whence the inode item is
         * the same on both snapshots.
         */
        if (sctx->cur_ino != sctx->cmp_key->objectid)
                return 0;

        if (!sctx->cur_inode_new_gen && !sctx->cur_inode_deleted) {
                if (result != BTRFS_COMPARE_TREE_DELETED)
                        ret = process_extent(sctx, sctx->left_path,
                                        sctx->cmp_key);
        }

        return ret;
}

static int changed_verity(struct send_ctx *sctx, enum btrfs_compare_tree_result result)
{
        if (!sctx->cur_inode_new_gen && !sctx->cur_inode_deleted) {
                if (result == BTRFS_COMPARE_TREE_NEW)
                        sctx->cur_inode_needs_verity = true;
        }
        return 0;
}

static int dir_changed(struct send_ctx *sctx, u64 dir)
{
        u64 orig_gen, new_gen;
        int ret;

        ret = get_inode_gen(sctx->send_root, dir, &new_gen);
        if (ret)
                return ret;

        ret = get_inode_gen(sctx->parent_root, dir, &orig_gen);
        if (ret)
                return ret;

        return (orig_gen != new_gen) ? 1 : 0;
}

static int compare_refs(struct send_ctx *sctx, struct btrfs_path *path,
                        struct btrfs_key *key)
{
        struct btrfs_inode_extref *extref;
        struct extent_buffer *leaf;
        u64 dirid = 0, last_dirid = 0;
        unsigned long ptr;
        u32 item_size;
        u32 cur_offset = 0;
        int ref_name_len;

        /* Easy case, just check this one dirid */
        if (key->type == BTRFS_INODE_REF_KEY) {
                dirid = key->offset;

                return dir_changed(sctx, dirid);
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size(leaf, path->slots[0]);
        ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
        while (cur_offset < item_size) {
                int ret;

                extref = (struct btrfs_inode_extref *)(ptr +
                                                       cur_offset);
                dirid = btrfs_inode_extref_parent(leaf, extref);
                ref_name_len = btrfs_inode_extref_name_len(leaf, extref);
                cur_offset += ref_name_len + sizeof(*extref);
                if (dirid == last_dirid)
                        continue;
                ret = dir_changed(sctx, dirid);
                if (ret)
                        return ret;
                last_dirid = dirid;
        }
        return 0;
}

/*
 * Updates compare related fields in sctx and simply forwards to the actual
 * changed_xxx functions.
 */
static int changed_cb(struct btrfs_path *left_path,
                      struct btrfs_path *right_path,
                      struct btrfs_key *key,
                      enum btrfs_compare_tree_result result,
                      struct send_ctx *sctx)
{
        int ret;

        /*
         * We can not hold the commit root semaphore here. This is because in
         * the case of sending and receiving to the same filesystem, using a
         * pipe, could result in a deadlock:
         *
         * 1) The task running send blocks on the pipe because it's full;
         *
         * 2) The task running receive, which is the only consumer of the pipe,
         *    is waiting for a transaction commit (for example due to a space
         *    reservation when doing a write or triggering a transaction commit
         *    when creating a subvolume);
         *
         * 3) The transaction is waiting to write lock the commit root semaphore,
         *    but can not acquire it since it's being held at 1).
         *
         * Down this call chain we write to the pipe through kernel_write().
         * The same type of problem can also happen when sending to a file that
         * is stored in the same filesystem - when reserving space for a write
         * into the file, we can trigger a transaction commit.
         *
         * Our caller has supplied us with clones of leaves from the send and
         * parent roots, so we're safe here from a concurrent relocation and
         * further reallocation of metadata extents while we are here. Below we
         * also assert that the leaves are clones.
         */
        lockdep_assert_not_held(&sctx->send_root->fs_info->commit_root_sem);

        /*
         * We always have a send root, so left_path is never NULL. We will not
         * have a leaf when we have reached the end of the send root but have
         * not yet reached the end of the parent root.
         */
        if (left_path->nodes[0])
                ASSERT(test_bit(EXTENT_BUFFER_UNMAPPED,
                                &left_path->nodes[0]->bflags));
        /*
         * When doing a full send we don't have a parent root, so right_path is
         * NULL. When doing an incremental send, we may have reached the end of
         * the parent root already, so we don't have a leaf at right_path.
         */
        if (right_path && right_path->nodes[0])
                ASSERT(test_bit(EXTENT_BUFFER_UNMAPPED,
                                &right_path->nodes[0]->bflags));

        if (result == BTRFS_COMPARE_TREE_SAME) {
                if (key->type == BTRFS_INODE_REF_KEY ||
                    key->type == BTRFS_INODE_EXTREF_KEY) {
                        ret = compare_refs(sctx, left_path, key);
                        if (!ret)
                                return 0;
                        if (ret < 0)
                                return ret;
                } else if (key->type == BTRFS_EXTENT_DATA_KEY) {
                        return maybe_send_hole(sctx, left_path, key);
                } else {
                        return 0;
                }
                result = BTRFS_COMPARE_TREE_CHANGED;
        }

        sctx->left_path = left_path;
        sctx->right_path = right_path;
        sctx->cmp_key = key;

        ret = finish_inode_if_needed(sctx, 0);
        if (ret < 0)
                return ret;

        /* Ignore non-FS objects */
        if (key->objectid == BTRFS_FREE_INO_OBJECTID ||
            key->objectid == BTRFS_FREE_SPACE_OBJECTID)
                return 0;

        if (key->type == BTRFS_INODE_ITEM_KEY) {
                ret = changed_inode(sctx, result);
        } else if (!sctx->ignore_cur_inode) {
                if (key->type == BTRFS_INODE_REF_KEY ||
                    key->type == BTRFS_INODE_EXTREF_KEY)
                        ret = changed_ref(sctx, result);
                else if (key->type == BTRFS_XATTR_ITEM_KEY)
                        ret = changed_xattr(sctx, result);
                else if (key->type == BTRFS_EXTENT_DATA_KEY)
                        ret = changed_extent(sctx, result);
                else if (key->type == BTRFS_VERITY_DESC_ITEM_KEY &&
                         key->offset == 0)
                        ret = changed_verity(sctx, result);
        }

        return ret;
}

static int search_key_again(const struct send_ctx *sctx,
                            struct btrfs_root *root,
                            struct btrfs_path *path,
                            const struct btrfs_key *key)
{
        int ret;

        if (!path->need_commit_sem)
                lockdep_assert_held_read(&root->fs_info->commit_root_sem);

        /*
         * Roots used for send operations are readonly and no one can add,
         * update or remove keys from them, so we should be able to find our
         * key again. The only exception is deduplication, which can operate on
         * readonly roots and add, update or remove keys to/from them - but at
         * the moment we don't allow it to run in parallel with send.
         */
        ret = btrfs_search_slot(NULL, root, key, path, 0, 0);
        ASSERT(ret <= 0);
        if (unlikely(ret > 0)) {
                btrfs_print_tree(path->nodes[path->lowest_level], false);
                btrfs_err(root->fs_info,
"send: key " BTRFS_KEY_FMT" not found in %s root %llu, lowest_level %d, slot %d",
                          BTRFS_KEY_FMT_VALUE(key),
                          (root == sctx->parent_root ? "parent" : "send"),
                          btrfs_root_id(root), path->lowest_level,
                          path->slots[path->lowest_level]);
                return -EUCLEAN;
        }

        return ret;
}

static int full_send_tree(struct send_ctx *sctx)
{
        int ret;
        struct btrfs_root *send_root = sctx->send_root;
        struct btrfs_key key;
        struct btrfs_fs_info *fs_info = send_root->fs_info;
        BTRFS_PATH_AUTO_FREE(path);

        path = alloc_path_for_send();
        if (!path)
                return -ENOMEM;
        path->reada = READA_FORWARD_ALWAYS;

        key.objectid = BTRFS_FIRST_FREE_OBJECTID;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;

        down_read(&fs_info->commit_root_sem);
        sctx->last_reloc_trans = fs_info->last_reloc_trans;
        up_read(&fs_info->commit_root_sem);

        ret = btrfs_search_slot_for_read(send_root, &key, path, 1, 0);
        if (ret < 0)
                return ret;
        if (ret)
                goto out_finish;

        while (1) {
                btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);

                ret = changed_cb(path, NULL, &key,
                                 BTRFS_COMPARE_TREE_NEW, sctx);
                if (ret < 0)
                        return ret;

                down_read(&fs_info->commit_root_sem);
                if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
                        sctx->last_reloc_trans = fs_info->last_reloc_trans;
                        up_read(&fs_info->commit_root_sem);
                        /*
                         * A transaction used for relocating a block group was
                         * committed or is about to finish its commit. Release
                         * our path (leaf) and restart the search, so that we
                         * avoid operating on any file extent items that are
                         * stale, with a disk_bytenr that reflects a pre
                         * relocation value. This way we avoid as much as
                         * possible to fallback to regular writes when checking
                         * if we can clone file ranges.
                         */
                        btrfs_release_path(path);
                        ret = search_key_again(sctx, send_root, path, &key);
                        if (ret < 0)
                                return ret;
                } else {
                        up_read(&fs_info->commit_root_sem);
                }

                ret = btrfs_next_item(send_root, path);
                if (ret < 0)
                        return ret;
                if (ret) {
                        ret  = 0;
                        break;
                }
        }

out_finish:
        return finish_inode_if_needed(sctx, 1);
}

static int replace_node_with_clone(struct btrfs_path *path, int level)
{
        struct extent_buffer *clone;

        clone = btrfs_clone_extent_buffer(path->nodes[level]);
        if (!clone)
                return -ENOMEM;

        free_extent_buffer(path->nodes[level]);
        path->nodes[level] = clone;

        return 0;
}

static int tree_move_down(struct btrfs_path *path, int *level, u64 reada_min_gen)
{
        struct extent_buffer *eb;
        struct extent_buffer *parent = path->nodes[*level];
        int slot = path->slots[*level];
        const int nritems = btrfs_header_nritems(parent);
        u64 reada_max;
        u64 reada_done = 0;

        lockdep_assert_held_read(&parent->fs_info->commit_root_sem);
        ASSERT(*level != 0);

        eb = btrfs_read_node_slot(parent, slot);
        if (IS_ERR(eb))
                return PTR_ERR(eb);

        /*
         * Trigger readahead for the next leaves we will process, so that it is
         * very likely that when we need them they are already in memory and we
         * will not block on disk IO. For nodes we only do readahead for one,
         * since the time window between processing nodes is typically larger.
         */
        reada_max = (*level == 1 ? SZ_128K : eb->fs_info->nodesize);

        for (slot++; slot < nritems && reada_done < reada_max; slot++) {
                if (btrfs_node_ptr_generation(parent, slot) > reada_min_gen) {
                        btrfs_readahead_node_child(parent, slot);
                        reada_done += eb->fs_info->nodesize;
                }
        }

        path->nodes[*level - 1] = eb;
        path->slots[*level - 1] = 0;
        (*level)--;

        if (*level == 0)
                return replace_node_with_clone(path, 0);

        return 0;
}

static int tree_move_next_or_upnext(struct btrfs_path *path,
                                    int *level, int root_level)
{
        int ret = 0;
        int nritems;
        nritems = btrfs_header_nritems(path->nodes[*level]);

        path->slots[*level]++;

        while (path->slots[*level] >= nritems) {
                if (*level == root_level) {
                        path->slots[*level] = nritems - 1;
                        return -1;
                }

                /* move upnext */
                path->slots[*level] = 0;
                free_extent_buffer(path->nodes[*level]);
                path->nodes[*level] = NULL;
                (*level)++;
                path->slots[*level]++;

                nritems = btrfs_header_nritems(path->nodes[*level]);
                ret = 1;
        }
        return ret;
}

/*
 * Returns 1 if it had to move up and next. 0 is returned if it moved only next
 * or down.
 */
static int tree_advance(struct btrfs_path *path,
                        int *level, int root_level,
                        int allow_down,
                        struct btrfs_key *key,
                        u64 reada_min_gen)
{
        int ret;

        if (*level == 0 || !allow_down) {
                ret = tree_move_next_or_upnext(path, level, root_level);
        } else {
                ret = tree_move_down(path, level, reada_min_gen);
        }

        /*
         * Even if we have reached the end of a tree, ret is -1, update the key
         * anyway, so that in case we need to restart due to a block group
         * relocation, we can assert that the last key of the root node still
         * exists in the tree.
         */
        if (*level == 0)
                btrfs_item_key_to_cpu(path->nodes[*level], key,
                                      path->slots[*level]);
        else
                btrfs_node_key_to_cpu(path->nodes[*level], key,
                                      path->slots[*level]);

        return ret;
}

static int tree_compare_item(struct btrfs_path *left_path,
                             struct btrfs_path *right_path,
                             char *tmp_buf)
{
        int cmp;
        int len1, len2;
        unsigned long off1, off2;

        len1 = btrfs_item_size(left_path->nodes[0], left_path->slots[0]);
        len2 = btrfs_item_size(right_path->nodes[0], right_path->slots[0]);
        if (len1 != len2)
                return 1;

        off1 = btrfs_item_ptr_offset(left_path->nodes[0], left_path->slots[0]);
        off2 = btrfs_item_ptr_offset(right_path->nodes[0],
                                right_path->slots[0]);

        read_extent_buffer(left_path->nodes[0], tmp_buf, off1, len1);

        cmp = memcmp_extent_buffer(right_path->nodes[0], tmp_buf, off2, len1);
        if (cmp)
                return 1;
        return 0;
}

/*
 * A transaction used for relocating a block group was committed or is about to
 * finish its commit. Release our paths and restart the search, so that we are
 * not using stale extent buffers:
 *
 * 1) For levels > 0, we are only holding references of extent buffers, without
 *    any locks on them, which does not prevent them from having been relocated
 *    and reallocated after the last time we released the commit root semaphore.
 *    The exception are the root nodes, for which we always have a clone, see
 *    the comment at btrfs_compare_trees();
 *
 * 2) For leaves, level 0, we are holding copies (clones) of extent buffers, so
 *    we are safe from the concurrent relocation and reallocation. However they
 *    can have file extent items with a pre relocation disk_bytenr value, so we
 *    restart the start from the current commit roots and clone the new leaves so
 *    that we get the post relocation disk_bytenr values. Not doing so, could
 *    make us clone the wrong data in case there are new extents using the old
 *    disk_bytenr that happen to be shared.
 */
static int restart_after_relocation(struct btrfs_path *left_path,
                                    struct btrfs_path *right_path,
                                    const struct btrfs_key *left_key,
                                    const struct btrfs_key *right_key,
                                    int left_level,
                                    int right_level,
                                    const struct send_ctx *sctx)
{
        int root_level;
        int ret;

        lockdep_assert_held_read(&sctx->send_root->fs_info->commit_root_sem);

        btrfs_release_path(left_path);
        btrfs_release_path(right_path);

        /*
         * Since keys can not be added or removed to/from our roots because they
         * are readonly and we do not allow deduplication to run in parallel
         * (which can add, remove or change keys), the layout of the trees should
         * not change.
         */
        left_path->lowest_level = left_level;
        ret = search_key_again(sctx, sctx->send_root, left_path, left_key);
        if (ret < 0)
                return ret;

        right_path->lowest_level = right_level;
        ret = search_key_again(sctx, sctx->parent_root, right_path, right_key);
        if (ret < 0)
                return ret;

        /*
         * If the lowest level nodes are leaves, clone them so that they can be
         * safely used by changed_cb() while not under the protection of the
         * commit root semaphore, even if relocation and reallocation happens in
         * parallel.
         */
        if (left_level == 0) {
                ret = replace_node_with_clone(left_path, 0);
                if (ret < 0)
                        return ret;
        }

        if (right_level == 0) {
                ret = replace_node_with_clone(right_path, 0);
                if (ret < 0)
                        return ret;
        }

        /*
         * Now clone the root nodes (unless they happen to be the leaves we have
         * already cloned). This is to protect against concurrent snapshotting of
         * the send and parent roots (see the comment at btrfs_compare_trees()).
         */
        root_level = btrfs_header_level(sctx->send_root->commit_root);
        if (root_level > 0) {
                ret = replace_node_with_clone(left_path, root_level);
                if (ret < 0)
                        return ret;
        }

        root_level = btrfs_header_level(sctx->parent_root->commit_root);
        if (root_level > 0) {
                ret = replace_node_with_clone(right_path, root_level);
                if (ret < 0)
                        return ret;
        }

        return 0;
}

/*
 * This function compares two trees and calls the provided callback for
 * every changed/new/deleted item it finds.
 * If shared tree blocks are encountered, whole subtrees are skipped, making
 * the compare pretty fast on snapshotted subvolumes.
 *
 * This currently works on commit roots only. As commit roots are read only,
 * we don't do any locking. The commit roots are protected with transactions.
 * Transactions are ended and rejoined when a commit is tried in between.
 *
 * This function checks for modifications done to the trees while comparing.
 * If it detects a change, it aborts immediately.
 */
static int btrfs_compare_trees(struct btrfs_root *left_root,
                        struct btrfs_root *right_root, struct send_ctx *sctx)
{
        struct btrfs_fs_info *fs_info = left_root->fs_info;
        int ret;
        int cmp;
        BTRFS_PATH_AUTO_FREE(left_path);
        BTRFS_PATH_AUTO_FREE(right_path);
        struct btrfs_key left_key;
        struct btrfs_key right_key;
        char *tmp_buf = NULL;
        int left_root_level;
        int right_root_level;
        int left_level;
        int right_level;
        int left_end_reached = 0;
        int right_end_reached = 0;
        int advance_left = 0;
        int advance_right = 0;
        u64 left_blockptr;
        u64 right_blockptr;
        u64 left_gen;
        u64 right_gen;
        u64 reada_min_gen;

        left_path = btrfs_alloc_path();
        if (!left_path) {
                ret = -ENOMEM;
                goto out;
        }
        right_path = btrfs_alloc_path();
        if (!right_path) {
                ret = -ENOMEM;
                goto out;
        }

        tmp_buf = kvmalloc(fs_info->nodesize, GFP_KERNEL);
        if (!tmp_buf) {
                ret = -ENOMEM;
                goto out;
        }

        left_path->search_commit_root = true;
        left_path->skip_locking = true;
        right_path->search_commit_root = true;
        right_path->skip_locking = true;

        /*
         * Strategy: Go to the first items of both trees. Then do
         *
         * If both trees are at level 0
         *   Compare keys of current items
         *     If left < right treat left item as new, advance left tree
         *       and repeat
         *     If left > right treat right item as deleted, advance right tree
         *       and repeat
         *     If left == right do deep compare of items, treat as changed if
         *       needed, advance both trees and repeat
         * If both trees are at the same level but not at level 0
         *   Compare keys of current nodes/leafs
         *     If left < right advance left tree and repeat
         *     If left > right advance right tree and repeat
         *     If left == right compare blockptrs of the next nodes/leafs
         *       If they match advance both trees but stay at the same level
         *         and repeat
         *       If they don't match advance both trees while allowing to go
         *         deeper and repeat
         * If tree levels are different
         *   Advance the tree that needs it and repeat
         *
         * Advancing a tree means:
         *   If we are at level 0, try to go to the next slot. If that's not
         *   possible, go one level up and repeat. Stop when we found a level
         *   where we could go to the next slot. We may at this point be on a
         *   node or a leaf.
         *
         *   If we are not at level 0 and not on shared tree blocks, go one
         *   level deeper.
         *
         *   If we are not at level 0 and on shared tree blocks, go one slot to
         *   the right if possible or go up and right.
         */

        down_read(&fs_info->commit_root_sem);
        left_level = btrfs_header_level(left_root->commit_root);
        left_root_level = left_level;
        /*
         * We clone the root node of the send and parent roots to prevent races
         * with snapshot creation of these roots. Snapshot creation COWs the
         * root node of a tree, so after the transaction is committed the old
         * extent can be reallocated while this send operation is still ongoing.
         * So we clone them, under the commit root semaphore, to be race free.
         */
        left_path->nodes[left_level] =
                        btrfs_clone_extent_buffer(left_root->commit_root);
        if (!left_path->nodes[left_level]) {
                ret = -ENOMEM;
                goto out_unlock;
        }

        right_level = btrfs_header_level(right_root->commit_root);
        right_root_level = right_level;
        right_path->nodes[right_level] =
                        btrfs_clone_extent_buffer(right_root->commit_root);
        if (!right_path->nodes[right_level]) {
                ret = -ENOMEM;
                goto out_unlock;
        }
        /*
         * Our right root is the parent root, while the left root is the "send"
         * root. We know that all new nodes/leaves in the left root must have
         * a generation greater than the right root's generation, so we trigger
         * readahead for those nodes and leaves of the left root, as we know we
         * will need to read them at some point.
         */
        reada_min_gen = btrfs_header_generation(right_root->commit_root);

        if (left_level == 0)
                btrfs_item_key_to_cpu(left_path->nodes[left_level],
                                &left_key, left_path->slots[left_level]);
        else
                btrfs_node_key_to_cpu(left_path->nodes[left_level],
                                &left_key, left_path->slots[left_level]);
        if (right_level == 0)
                btrfs_item_key_to_cpu(right_path->nodes[right_level],
                                &right_key, right_path->slots[right_level]);
        else
                btrfs_node_key_to_cpu(right_path->nodes[right_level],
                                &right_key, right_path->slots[right_level]);

        sctx->last_reloc_trans = fs_info->last_reloc_trans;

        while (1) {
                if (need_resched() ||
                    rwsem_is_contended(&fs_info->commit_root_sem)) {
                        up_read(&fs_info->commit_root_sem);
                        cond_resched();
                        down_read(&fs_info->commit_root_sem);
                }

                if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
                        ret = restart_after_relocation(left_path, right_path,
                                                       &left_key, &right_key,
                                                       left_level, right_level,
                                                       sctx);
                        if (ret < 0)
                                goto out_unlock;
                        sctx->last_reloc_trans = fs_info->last_reloc_trans;
                }

                if (advance_left && !left_end_reached) {
                        ret = tree_advance(left_path, &left_level,
                                        left_root_level,
                                        advance_left != ADVANCE_ONLY_NEXT,
                                        &left_key, reada_min_gen);
                        if (ret == -1)
                                left_end_reached = ADVANCE;
                        else if (ret < 0)
                                goto out_unlock;
                        advance_left = 0;
                }
                if (advance_right && !right_end_reached) {
                        ret = tree_advance(right_path, &right_level,
                                        right_root_level,
                                        advance_right != ADVANCE_ONLY_NEXT,
                                        &right_key, reada_min_gen);
                        if (ret == -1)
                                right_end_reached = ADVANCE;
                        else if (ret < 0)
                                goto out_unlock;
                        advance_right = 0;
                }

                if (left_end_reached && right_end_reached) {
                        ret = 0;
                        goto out_unlock;
                } else if (left_end_reached) {
                        if (right_level == 0) {
                                up_read(&fs_info->commit_root_sem);
                                ret = changed_cb(left_path, right_path,
                                                &right_key,
                                                BTRFS_COMPARE_TREE_DELETED,
                                                sctx);
                                if (ret < 0)
                                        goto out;
                                down_read(&fs_info->commit_root_sem);
                        }
                        advance_right = ADVANCE;
                        continue;
                } else if (right_end_reached) {
                        if (left_level == 0) {
                                up_read(&fs_info->commit_root_sem);
                                ret = changed_cb(left_path, right_path,
                                                &left_key,
                                                BTRFS_COMPARE_TREE_NEW,
                                                sctx);
                                if (ret < 0)
                                        goto out;
                                down_read(&fs_info->commit_root_sem);
                        }
                        advance_left = ADVANCE;
                        continue;
                }

                if (left_level == 0 && right_level == 0) {
                        up_read(&fs_info->commit_root_sem);
                        cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
                        if (cmp < 0) {
                                ret = changed_cb(left_path, right_path,
                                                &left_key,
                                                BTRFS_COMPARE_TREE_NEW,
                                                sctx);
                                advance_left = ADVANCE;
                        } else if (cmp > 0) {
                                ret = changed_cb(left_path, right_path,
                                                &right_key,
                                                BTRFS_COMPARE_TREE_DELETED,
                                                sctx);
                                advance_right = ADVANCE;
                        } else {
                                enum btrfs_compare_tree_result result;

                                WARN_ON(!extent_buffer_uptodate(left_path->nodes[0]));
                                ret = tree_compare_item(left_path, right_path,
                                                        tmp_buf);
                                if (ret)
                                        result = BTRFS_COMPARE_TREE_CHANGED;
                                else
                                        result = BTRFS_COMPARE_TREE_SAME;
                                ret = changed_cb(left_path, right_path,
                                                 &left_key, result, sctx);
                                advance_left = ADVANCE;
                                advance_right = ADVANCE;
                        }

                        if (ret < 0)
                                goto out;
                        down_read(&fs_info->commit_root_sem);
                } else if (left_level == right_level) {
                        cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
                        if (cmp < 0) {
                                advance_left = ADVANCE;
                        } else if (cmp > 0) {
                                advance_right = ADVANCE;
                        } else {
                                left_blockptr = btrfs_node_blockptr(
                                                left_path->nodes[left_level],
                                                left_path->slots[left_level]);
                                right_blockptr = btrfs_node_blockptr(
                                                right_path->nodes[right_level],
                                                right_path->slots[right_level]);
                                left_gen = btrfs_node_ptr_generation(
                                                left_path->nodes[left_level],
                                                left_path->slots[left_level]);
                                right_gen = btrfs_node_ptr_generation(
                                                right_path->nodes[right_level],
                                                right_path->slots[right_level]);
                                if (left_blockptr == right_blockptr &&
                                    left_gen == right_gen) {
                                        /*
                                         * As we're on a shared block, don't
                                         * allow to go deeper.
                                         */
                                        advance_left = ADVANCE_ONLY_NEXT;
                                        advance_right = ADVANCE_ONLY_NEXT;
                                } else {
                                        advance_left = ADVANCE;
                                        advance_right = ADVANCE;
                                }
                        }
                } else if (left_level < right_level) {
                        advance_right = ADVANCE;
                } else {
                        advance_left = ADVANCE;
                }
        }

out_unlock:
        up_read(&fs_info->commit_root_sem);
out:
        kvfree(tmp_buf);
        return ret;
}

static int send_subvol(struct send_ctx *sctx)
{
        int ret;

        if (!(sctx->flags & BTRFS_SEND_FLAG_OMIT_STREAM_HEADER)) {
                ret = send_header(sctx);
                if (ret < 0)
                        goto out;
        }

        ret = send_subvol_begin(sctx);
        if (ret < 0)
                goto out;

        if (sctx->parent_root) {
                ret = btrfs_compare_trees(sctx->send_root, sctx->parent_root, sctx);
                if (ret < 0)
                        goto out;
                ret = finish_inode_if_needed(sctx, 1);
                if (ret < 0)
                        goto out;
        } else {
                ret = full_send_tree(sctx);
                if (ret < 0)
                        goto out;
        }

out:
        free_recorded_refs(sctx);
        return ret;
}

/*
 * If orphan cleanup did remove any orphans from a root, it means the tree
 * was modified and therefore the commit root is not the same as the current
 * root anymore. This is a problem, because send uses the commit root and
 * therefore can see inode items that don't exist in the current root anymore,
 * and for example make calls to btrfs_iget, which will do tree lookups based
 * on the current root and not on the commit root. Those lookups will fail,
 * returning a -ESTALE error, and making send fail with that error. So make
 * sure a send does not see any orphans we have just removed, and that it will
 * see the same inodes regardless of whether a transaction commit happened
 * before it started (meaning that the commit root will be the same as the
 * current root) or not.
 */
static int ensure_commit_roots_uptodate(struct send_ctx *sctx)
{
        struct btrfs_root *root = sctx->parent_root;

        if (root && root->node != root->commit_root)
                return btrfs_commit_current_transaction(root);

        for (int i = 0; i < sctx->clone_roots_cnt; i++) {
                root = sctx->clone_roots[i].root;
                if (root->node != root->commit_root)
                        return btrfs_commit_current_transaction(root);
        }

        return 0;
}

/*
 * Make sure any existing delalloc is flushed for any root used by a send
 * operation so that we do not miss any data and we do not race with writeback
 * finishing and changing a tree while send is using the tree. This could
 * happen if a subvolume is in RW mode, has delalloc, is turned to RO mode and
 * a send operation then uses the subvolume.
 * After flushing delalloc ensure_commit_roots_uptodate() must be called.
 */
static int flush_delalloc_roots(struct send_ctx *sctx)
{
        struct btrfs_root *root = sctx->parent_root;
        int ret;
        int i;

        if (root) {
                ret = btrfs_start_delalloc_snapshot(root, false);
                if (ret)
                        return ret;
                btrfs_wait_ordered_extents(root, U64_MAX, NULL);
        }

        for (i = 0; i < sctx->clone_roots_cnt; i++) {
                root = sctx->clone_roots[i].root;
                ret = btrfs_start_delalloc_snapshot(root, false);
                if (ret)
                        return ret;
                btrfs_wait_ordered_extents(root, U64_MAX, NULL);
        }

        return 0;
}

static void btrfs_root_dec_send_in_progress(struct btrfs_root* root)
{
        spin_lock(&root->root_item_lock);
        root->send_in_progress--;
        /*
         * Not much left to do, we don't know why it's unbalanced and
         * can't blindly reset it to 0.
         */
        if (root->send_in_progress < 0)
                btrfs_err(root->fs_info,
                          "send_in_progress unbalanced %d root %llu",
                          root->send_in_progress, btrfs_root_id(root));
        spin_unlock(&root->root_item_lock);
}

static void dedupe_in_progress_warn(const struct btrfs_root *root)
{
        btrfs_warn_rl(root->fs_info,
"cannot use root %llu for send while deduplications on it are in progress (%d in progress)",
                      btrfs_root_id(root), root->dedupe_in_progress);
}

long btrfs_ioctl_send(struct btrfs_root *send_root, const struct btrfs_ioctl_send_args *arg)
{
        int ret = 0;
        struct btrfs_fs_info *fs_info = send_root->fs_info;
        struct btrfs_root *clone_root;
        struct send_ctx *sctx = NULL;
        u32 i;
        u64 *clone_sources_tmp = NULL;
        int clone_sources_to_rollback = 0;
        size_t alloc_size;
        int sort_clone_roots = 0;
        struct btrfs_lru_cache_entry *entry;
        struct btrfs_lru_cache_entry *tmp;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        /*
         * The subvolume must remain read-only during send, protect against
         * making it RW. This also protects against deletion.
         */
        spin_lock(&send_root->root_item_lock);
        /*
         * Unlikely but possible, if the subvolume is marked for deletion but
         * is slow to remove the directory entry, send can still be started.
         */
        if (btrfs_root_dead(send_root)) {
                spin_unlock(&send_root->root_item_lock);
                return -EPERM;
        }
        /* Userspace tools do the checks and warn the user if it's not RO. */
        if (!btrfs_root_readonly(send_root)) {
                spin_unlock(&send_root->root_item_lock);
                return -EPERM;
        }
        if (send_root->dedupe_in_progress) {
                dedupe_in_progress_warn(send_root);
                spin_unlock(&send_root->root_item_lock);
                return -EAGAIN;
        }
        send_root->send_in_progress++;
        spin_unlock(&send_root->root_item_lock);

        /*
         * Check that we don't overflow at later allocations, we request
         * clone_sources_count + 1 items, and compare to unsigned long inside
         * access_ok. Also set an upper limit for allocation size so this can't
         * easily exhaust memory. Max number of clone sources is about 200K.
         */
        if (arg->clone_sources_count > SZ_8M / sizeof(struct clone_root)) {
                ret = -EINVAL;
                goto out;
        }

        if (arg->flags & ~BTRFS_SEND_FLAG_MASK) {
                ret = -EOPNOTSUPP;
                goto out;
        }

        sctx = kzalloc_obj(struct send_ctx);
        if (!sctx) {
                ret = -ENOMEM;
                goto out;
        }

        init_path(&sctx->cur_inode_path);
        INIT_LIST_HEAD(&sctx->new_refs);
        INIT_LIST_HEAD(&sctx->deleted_refs);

        btrfs_lru_cache_init(&sctx->name_cache, SEND_MAX_NAME_CACHE_SIZE);
        btrfs_lru_cache_init(&sctx->backref_cache, SEND_MAX_BACKREF_CACHE_SIZE);
        btrfs_lru_cache_init(&sctx->dir_created_cache,
                             SEND_MAX_DIR_CREATED_CACHE_SIZE);
        /*
         * This cache is periodically trimmed to a fixed size elsewhere, see
         * cache_dir_utimes() and trim_dir_utimes_cache().
         */
        btrfs_lru_cache_init(&sctx->dir_utimes_cache, 0);

        sctx->pending_dir_moves = RB_ROOT;
        sctx->waiting_dir_moves = RB_ROOT;
        sctx->orphan_dirs = RB_ROOT;
        sctx->rbtree_new_refs = RB_ROOT;
        sctx->rbtree_deleted_refs = RB_ROOT;

        sctx->flags = arg->flags;

        if (arg->flags & BTRFS_SEND_FLAG_VERSION) {
                if (arg->version > BTRFS_SEND_STREAM_VERSION) {
                        ret = -EPROTO;
                        goto out;
                }
                /* Zero means "use the highest version" */
                sctx->proto = arg->version ?: BTRFS_SEND_STREAM_VERSION;
        } else {
                sctx->proto = 1;
        }
        if ((arg->flags & BTRFS_SEND_FLAG_COMPRESSED) && sctx->proto < 2) {
                ret = -EINVAL;
                goto out;
        }

        sctx->send_filp = fget(arg->send_fd);
        if (!sctx->send_filp || !(sctx->send_filp->f_mode & FMODE_WRITE)) {
                ret = -EBADF;
                goto out;
        }

        sctx->send_root = send_root;
        sctx->clone_roots_cnt = arg->clone_sources_count;

        if (sctx->proto >= 2) {
                u32 send_buf_num_pages;

                sctx->send_max_size = BTRFS_SEND_BUF_SIZE_V2;
                sctx->send_buf = vmalloc(sctx->send_max_size);
                if (!sctx->send_buf) {
                        ret = -ENOMEM;
                        goto out;
                }
                send_buf_num_pages = sctx->send_max_size >> PAGE_SHIFT;
                sctx->send_buf_pages = kzalloc_objs(*sctx->send_buf_pages,
                                                    send_buf_num_pages);
                if (!sctx->send_buf_pages) {
                        ret = -ENOMEM;
                        goto out;
                }
                for (i = 0; i < send_buf_num_pages; i++) {
                        sctx->send_buf_pages[i] =
                                vmalloc_to_page(sctx->send_buf + (i << PAGE_SHIFT));
                }
        } else {
                sctx->send_max_size = BTRFS_SEND_BUF_SIZE_V1;
                sctx->send_buf = kvmalloc(sctx->send_max_size, GFP_KERNEL);
        }
        if (!sctx->send_buf) {
                ret = -ENOMEM;
                goto out;
        }

        sctx->clone_roots = kvzalloc_objs(*sctx->clone_roots,
                                          arg->clone_sources_count + 1);
        if (!sctx->clone_roots) {
                ret = -ENOMEM;
                goto out;
        }

        alloc_size = array_size(sizeof(*arg->clone_sources),
                                arg->clone_sources_count);

        if (arg->clone_sources_count) {
                clone_sources_tmp = kvmalloc(alloc_size, GFP_KERNEL);
                if (!clone_sources_tmp) {
                        ret = -ENOMEM;
                        goto out;
                }

                ret = copy_from_user(clone_sources_tmp, arg->clone_sources,
                                alloc_size);
                if (ret) {
                        ret = -EFAULT;
                        goto out;
                }

                for (i = 0; i < arg->clone_sources_count; i++) {
                        clone_root = btrfs_get_fs_root(fs_info,
                                                clone_sources_tmp[i], true);
                        if (IS_ERR(clone_root)) {
                                ret = PTR_ERR(clone_root);
                                goto out;
                        }
                        spin_lock(&clone_root->root_item_lock);
                        if (!btrfs_root_readonly(clone_root) ||
                            btrfs_root_dead(clone_root)) {
                                spin_unlock(&clone_root->root_item_lock);
                                btrfs_put_root(clone_root);
                                ret = -EPERM;
                                goto out;
                        }
                        if (clone_root->dedupe_in_progress) {
                                dedupe_in_progress_warn(clone_root);
                                spin_unlock(&clone_root->root_item_lock);
                                btrfs_put_root(clone_root);
                                ret = -EAGAIN;
                                goto out;
                        }
                        clone_root->send_in_progress++;
                        spin_unlock(&clone_root->root_item_lock);

                        sctx->clone_roots[i].root = clone_root;
                        clone_sources_to_rollback = i + 1;
                }
                kvfree(clone_sources_tmp);
                clone_sources_tmp = NULL;
        }

        if (arg->parent_root) {
                sctx->parent_root = btrfs_get_fs_root(fs_info, arg->parent_root,
                                                      true);
                if (IS_ERR(sctx->parent_root)) {
                        ret = PTR_ERR(sctx->parent_root);
                        goto out;
                }

                spin_lock(&sctx->parent_root->root_item_lock);
                sctx->parent_root->send_in_progress++;
                if (!btrfs_root_readonly(sctx->parent_root) ||
                                btrfs_root_dead(sctx->parent_root)) {
                        spin_unlock(&sctx->parent_root->root_item_lock);
                        ret = -EPERM;
                        goto out;
                }
                if (sctx->parent_root->dedupe_in_progress) {
                        dedupe_in_progress_warn(sctx->parent_root);
                        spin_unlock(&sctx->parent_root->root_item_lock);
                        ret = -EAGAIN;
                        goto out;
                }
                spin_unlock(&sctx->parent_root->root_item_lock);
        }

        /*
         * Clones from send_root are allowed, but only if the clone source
         * is behind the current send position. This is checked while searching
         * for possible clone sources.
         */
        sctx->clone_roots[sctx->clone_roots_cnt++].root =
                btrfs_grab_root(sctx->send_root);

        /* We do a bsearch later */
        sort(sctx->clone_roots, sctx->clone_roots_cnt,
                        sizeof(*sctx->clone_roots), __clone_root_cmp_sort,
                        NULL);
        sort_clone_roots = 1;

        ret = flush_delalloc_roots(sctx);
        if (ret)
                goto out;

        ret = ensure_commit_roots_uptodate(sctx);
        if (ret)
                goto out;

        ret = send_subvol(sctx);
        if (ret < 0)
                goto out;

        btrfs_lru_cache_for_each_entry_safe(&sctx->dir_utimes_cache, entry, tmp) {
                ret = send_utimes(sctx, entry->key, entry->gen);
                if (ret < 0)
                        goto out;
                btrfs_lru_cache_remove(&sctx->dir_utimes_cache, entry);
        }

        if (!(sctx->flags & BTRFS_SEND_FLAG_OMIT_END_CMD)) {
                ret = begin_cmd(sctx, BTRFS_SEND_C_END);
                if (ret < 0)
                        goto out;
                ret = send_cmd(sctx);
                if (ret < 0)
                        goto out;
        }

out:
        WARN_ON(sctx && !ret && !RB_EMPTY_ROOT(&sctx->pending_dir_moves));
        while (sctx && !RB_EMPTY_ROOT(&sctx->pending_dir_moves)) {
                struct rb_node *n;
                struct pending_dir_move *pm;

                n = rb_first(&sctx->pending_dir_moves);
                pm = rb_entry(n, struct pending_dir_move, node);
                while (!list_empty(&pm->list)) {
                        struct pending_dir_move *pm2;

                        pm2 = list_first_entry(&pm->list,
                                               struct pending_dir_move, list);
                        free_pending_move(sctx, pm2);
                }
                free_pending_move(sctx, pm);
        }

        WARN_ON(sctx && !ret && !RB_EMPTY_ROOT(&sctx->waiting_dir_moves));
        while (sctx && !RB_EMPTY_ROOT(&sctx->waiting_dir_moves)) {
                struct rb_node *n;
                struct waiting_dir_move *dm;

                n = rb_first(&sctx->waiting_dir_moves);
                dm = rb_entry(n, struct waiting_dir_move, node);
                rb_erase(&dm->node, &sctx->waiting_dir_moves);
                kfree(dm);
        }

        WARN_ON(sctx && !ret && !RB_EMPTY_ROOT(&sctx->orphan_dirs));
        while (sctx && !RB_EMPTY_ROOT(&sctx->orphan_dirs)) {
                struct rb_node *n;
                struct orphan_dir_info *odi;

                n = rb_first(&sctx->orphan_dirs);
                odi = rb_entry(n, struct orphan_dir_info, node);
                free_orphan_dir_info(sctx, odi);
        }

        if (sort_clone_roots) {
                for (i = 0; i < sctx->clone_roots_cnt; i++) {
                        btrfs_root_dec_send_in_progress(
                                        sctx->clone_roots[i].root);
                        btrfs_put_root(sctx->clone_roots[i].root);
                }
        } else {
                for (i = 0; sctx && i < clone_sources_to_rollback; i++) {
                        btrfs_root_dec_send_in_progress(
                                        sctx->clone_roots[i].root);
                        btrfs_put_root(sctx->clone_roots[i].root);
                }

                btrfs_root_dec_send_in_progress(send_root);
        }
        if (sctx && !IS_ERR_OR_NULL(sctx->parent_root)) {
                btrfs_root_dec_send_in_progress(sctx->parent_root);
                btrfs_put_root(sctx->parent_root);
        }

        kvfree(clone_sources_tmp);

        if (sctx) {
                if (sctx->send_filp)
                        fput(sctx->send_filp);

                kvfree(sctx->clone_roots);
                kfree(sctx->send_buf_pages);
                kvfree(sctx->send_buf);
                kvfree(sctx->verity_descriptor);

                close_current_inode(sctx);

                btrfs_lru_cache_clear(&sctx->name_cache);
                btrfs_lru_cache_clear(&sctx->backref_cache);
                btrfs_lru_cache_clear(&sctx->dir_created_cache);
                btrfs_lru_cache_clear(&sctx->dir_utimes_cache);

                if (sctx->cur_inode_path.buf != sctx->cur_inode_path.inline_buf)
                        kfree(sctx->cur_inode_path.buf);

                kfree(sctx);
        }

        return ret;
}